To:	Users
From:	Bob Supnik
Subj:	18b PDP Simulator Usage
Date:	25-Aug-2003

			COPYRIGHT NOTICE

The following copyright notice applies to both the SIMH source and binary:

   Original code published in 1993-2003, written by Robert M Supnik
   Copyright (c) 1993-2003, Robert M Supnik

   Permission is hereby granted, free of charge, to any person obtaining a
   copy of this software and associated documentation files (the "Software"),
   to deal in the Software without restriction, including without limitation
   the rights to use, copy, modify, merge, publish, distribute, sublicense,
   and/or sell copies of the Software, and to permit persons to whom the
   Software is furnished to do so, subject to the following conditions:

   The above copyright notice and this permission notice shall be included in
   all copies or substantial portions of the Software.

   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
   ROBERT M SUPNIK BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
   IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
   CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

   Except as contained in this notice, the name of Robert M Supnik shall not
   be used in advertising or otherwise to promote the sale, use or other dealings
   in this Software without prior written authorization from Robert M Supnik.

This memorandum documents the PDP-4, PDP-7, PDP-9, and PDP-15 simulators.


1. Simulator Files

To compile a particular model in the 18b family, you must include the appropriate
switch in the compilation command line:

PDP-4/		PDP4
PDP-7/		PDP7
PDP-9/		PDP9
PDP-15/		PDP15

If no model is specified, the default is the PDP-15.

				      PDP-4   PDP-7   PDP-9   PDP-15
sim/		sim_defs.h		x	x	x	x
		sim_rev.h		x	x	x	x
		sim_sock.h		x	x	x	x
		sim_tape.h				x	x
		sim_tmxr.h		x	x	x	x
		scp.c			x	x	x	x
		scp_tty.c		x	x	x	x
		sim_sock.c		x	x	x	x
		sim_tape.c				x	x
		sim_tmxr.c		x	x	x	x

sim/pdp18b/	pdp18b_defs.h		x	x	x	x
		pdp18b_cpu.c		x	x	x	x
		pdp18b_drm.c		x	x
		pdp18b_dt.c		x	x	x	x
		pdp18b_fpp.c					x
		pdp18b_lp.c		x	x	x	x
		pdp18b_mt.c				x	x
		pdp18b_rb.c				x
		pdp18b_rf.c				x	x
		pdp18b_rp.c					x
		pdp18b_stddev.c		x	x	x	x
		pdp18b_sys.c		x	x	x	x
		pdp18b_tt1.c				x	x

2. 18b PDP Features

The other four 18b PDP's (PDP-4, PDP-7, PDP-9, PDP-15) are very similar
and are configured as follows:

system	device		simulates
	name(s)

PDP-4	CPU		PDP-4 CPU with 8KW of memory
	-		Type 18 extended arithmetic element (EAE)
	PTR,PTP		integral paper tape/Type 75 punch
	TTI,TTO		KSR28 console terminal (Baudot code)
	LPT		Type 62 line printer (Hollerith code)
	CLK		integral real-time clock
	DT		Type 550/555 DECtape
	DRM		Type 24 serial drum

PDP-7	CPU		PDP-7 CPU with 32KW of memory
	-		Type 177 extended arithmetic element (EAE)
	-		Type 148 memory extension
	PTR,PTP		Type 444 paper tape reader/Type 75 punch
	TTI,TTO		KSR 33 console terminal
	LPT		Type 647 line printer
	CLK		integral real-time clock
	DT		Type 550/555 DECtape
	DRM		Type 24 serial drum

PDP-9	CPU		PDP-9 CPU with 32KW of memory
	-		KE09A extended arithmetic element (EAE)
	-		KF09A automatic priority interrupt (API)
	-		KG09B memory extension
	-		KP09A power detection
	-		KX09A memory protection
	PTR,PTP		PC09A paper tape reader/punch
	TTI,TTO		KSR 33 console terminal
	TTI1,TTO1	LT09A second console terminal
	LP9		LP09 line printer
	LPT		Type 647E line printer
	CLK		integral real-time clock
	RB		RB09 fixed-head disk
	RF		RF09/RS09 fixed-head disk
	DT		TC02/TU55 DECtape
	MT		TC59/TU10 magnetic tape

PDP-15	CPU		PDP-15 CPU with 32KW of memory
	-		KE15 extended arithmetic element (EAE)
	-		KA15 automatic priority interrupt (API)
	-		KF15 power detection
	-		KM15 memory protection
	-		KT15 memory relocation and protection
	-		XVM memory relocation and protection
	FPP		FP15 floating point processor
	PTR,PTP		PC15 paper tape reader/punch
	TTI,TTO		KSR 35 console terminal
	TTI1,TTO1	LT15 second console terminal
	LP9		LP09 line printer
	LPT		LP15 line printer
	CLK		integral real-time clock
	RP		RP15/RP02 disk pack
	RF		RF15/RS09 fixed-head disk
	DT		TC15/TU56 DECtape
	MT		TC59/TU10 magnetic tape

Most devices can be disabled or enabled, by the commands:

	SET <dev> DISABLED
	SET <dev> ENABLED

The simulator allows most device numbers to be changed, by the command:

	SET <dev> DEV=<number>

However, devices can only be BOOTed with their default device numbers.

The 18b PDP simulators implement several unique stop conditions:

	- an unimplemented instruction is decoded, and register
	  STOP_INST is set
	- more than XCT_MAX nested executes are detected during
	  instruction execution
	- an FP15 instruction is decoded, the FP15 is disabled,
	  and register STOP_FPP is set

The PDP-4 and PDP-7 LOAD command supports only "second stage" RIM format
files (alternating DAC address instructions and data):

	LOAD file			load PDP-4/PDP-7 RIM format file

The PDP-9 and PDP-15 LOAD commands support hardware RIM format (data only),
PDP-4/PDP-7 RIM loader format (for compatability with Macro7), and BIN
loader format:

	LOAD -S file			load PDP-4/PDP-7 RIM format file
	LOAD -R file address		load PDP-9/PDP-15 RIM format
					  file starting at address
	LOAD file.RIM address		assume file is PDP-9/PDP-15
					  RIM format
	LOAD -B file			load PDP-9/PDP-15 BIN format file
	LOAD file.BIN			assume file is PDP-9/PDP-15
					  BIN format

If no address is given for a RIM format load, a starting address of 200
(octal) is assumed.  If no switch is specified, and the file extension is
neither RIM nor BIN, the file format is assumed to be BIN.

2.1 CPU

The CPU options are the presence of the EAE, the presense of the API and
memory protection (for the PDP-9 and PDP-15), the presense of relocation
or XVM (PDP-15 only), and the size of main memory.

	system	option			comment

	all	SET CPU EAE		enable EAE
	all	SET CPU NOEAE		disable EAE
	9,15	SET CPU API		enable API
	9,15	SET CPU NOAPI		disable API
	9,15	SET CPU PROT		enable memory protection
	15	SET CPU RELOC		enable memory relocation
	15	SET CPU XVM		enable XVM relocation
	9,15	SET CPU NOPROT		disable protection, relocation, XVM
	4	SET CPU 4K		set memory size = 4K
	all	SET CPU 8K		set memory size = 8K
	all	SET CPU 12K		set memory size = 12K
	all	SET CPU 16K		set memory size = 16K
	all	SET CPU 20K		set memory size = 20K
	all	SET CPU 24K		set memory size = 24K
	all	SET CPU 28K		set memory size = 28K
	all	SET CPU 32K		set memory size = 32K
	15	SET CPU 48K		set memory size = 48K
	15	SET CPU 64K		set memory size = 64K
	15	SET CPU 80K		set memory size = 80K
	15	SET CPU 96K		set memory size = 96K
	15	SET CPU 112K		set memory size = 112K
	15	SET CPU 128K		set memory size = 128K

Memory sizes greater than 8K are only available on the PDP-7, PDP-9, and
PDP-15; memory sizes greater than 32KW are only available on the PDP-15.
If memory size is being reduced, and the memory being truncated contains
non-zero data, the simulator asks for confirmation.  Data in the truncated
portion of memory is lost.  Initial memory size is 8K for the PDP-4, 32K
for the PDP-7 and PDP-9, and 128K for the PDP-15.

The PROT option corresponds to the KX09A on the PDP-9 and the KM15 for the
PDP-15.  The PROT option is required to run the Foreground/Background
Monitor.  The RELOC option corresponds to the KT15 on the PDP-15, and the
XVM option corresponds to the XM15 on the PDP-15.  ADSS-15, ADSS-15 Foreground/
Background, and standard DOS-15 will <not> run if these options are enabled.

CPU registers include the visible state of the processor as well as the
control registers for the interrupt system.

	system	name		size	comments

	all	PC		addr	program counter
	all	AC		18	accumulator
	all	L		1	link
	all	MQ		18	multiplier-quotient
	all	SC		6	shift counter
	all	EAE_AC_SIGN	1	EAE AC sign
	all	SR		18	front panel switches
	all	ASW		addr	address switches for RIM load
	all	INT[0:4]	32	interrupt requests,
					0:3 = API levels 0-3
					4 = PI level
	all	IORS		18	IORS register
	all	ION		1	interrupt enable
	all	ION_DELAY	2	interrupt enable delay
	15	ION_INH		1	interrupt inhibit
	9,15	APIENB		1	API enable
	9,15	APIREQ		8	API requesting levels
	9,15	APIACT		8	API active levels
	9,15	BR		18	memory protection bounds
	15	XR		18	index register
	15	LR		18	limit register
	9,15	BR		18	memory protection bounds
	15	RR		18	memory protection relocation
	15	MMR		18	memory protection control
	9,15	USMD		1	user mode
	9,15	USMDBUF		1	user mode buffer
	9,15	USMDDEF		1	user mode load defer
	9,15	NEXM		1	non-existent memory violation
	9,15	PRVN		1	privilege violation
	7,9	EXTM		1	extend mode
	7,9	EXTM_INIT	1	extend mode value after reset
	15	BANKM		1	bank mode
	15	BANKM_INIT	1	bank mode value after reset
	7	TRAPM		1	trap mode
	7,9,15	TRAPP		1	trap pending
	7,9	EMIRP		1	EMIR instruction pending
	9,15	RESTP		1	DBR or RES instruction pending
	9,15	PWRFL		1	power fail flag
	all	PCQ[0:63]	addr	PC prior to last JMP, JMS, CAL, or
					interrupt; most recent PC change first
	all	STOP_INST	1	stop on undefined instruction
	all	XCT_MAX		8	maximum number of chained XCT's allowed
	all	WRU		8	interrupt character

"addr" signifies the address width of the system (13b for the PDP-4, 15b for
the PDP-7 and PDP-9, 17b for the PDP-15).

2.2 Floating Point Processor (FPP)

The PDP-15 features an optional floating point processor, the FP15 (FPP).
The FPP can be enabled and disabled; by default it is disabled.

The FPP implements these registers:

	name		size	comments

	FIR		12	floating instruction register
	EPA		18	EPA (A exponent)
	FMAS		1	FMA sign
	FMAH		17	FMA<1:17>
	FMAL		18	FMA<18:35>
	EPB		18	EPB (B exponent)
	FMBS		1	FMB sign
	FMBH		17	FMB<1:17>
	FMBL		18	FMB<18:35>
	FGUARD		1	guard bit
	FMQH		17	FMQ<1:17>
	FMQL		18	FMQ<18:35>
	JEA		18	exception address register
	STOP_FPP	1	stop if FP15 instruction decoded
				while FP15 is disabled

2.3 Programmed I/O Devices

2.3.1 Paper Tape Reader (PTR)

The paper tape reader (PTR) reads data from a disk file.  The POS
register specifies the number of the next data item to be read.  Thus,
by changing POS, the user can backspace or advance the reader.

The paper tape reader supports the BOOT command.  The specific forms
recognized vary from system to system:

	BOOT PTR	PDP-4, PDP-7: load RIM loader and start it running
	BOOT -F PTR	PDP-4, PDP-7: load funny format loader and start
			  it running
	BOOT -H PTR	PDP-7: start hardware RIM load at address given
			  by address switches (ASW)
	BOOT {-H} PTR	PDP-9, PDP-15: start hardware RIM load at address
			  given by address switches (ASW)

The PDP-4 did not have a hardware read-in mode load capability.

The PTR ATTACH command recognizes one switch, -A for ASCII mode.  In
ASCII mode, data returned by the read alphabetic command has even parity.
This allows normal text files to be used as input to the paper tape reader.

The paper tape reader implements these registers:

	name		size	comments

	BUF		8	last data item processed
	INT		1	interrupt pending flag
	DONE		1	device done flag
	ERR		1	error flag (PDP-9, PDP-15 only)
	POS		32	position in the input file
	TIME		24	time from I/O initiation to interrupt
	STOP_IOE	1	stop on I/O error

Error handling is as follows:

	error	     STOP_IOE	processed as

	not attached	1	report error and stop
			0	out of tape

	end of file	1	report error and stop
			0	out of tape

	OS I/O error	x	report error and stop

2.3.2 Paper Tape Punch (PTP)

The paper tape punch (PTP) writes data to a disk file.  The POS
register specifies the number of the next data item to be written.
Thus, by changing POS, the user can backspace or advance the punch.

The PTP ATTACH command recognizes one switch, -A for ASCII mode.  In
ASCII mode, data is punched with the high order bit clear, and NULL and
DEL characters are supressed.  This allows punch output to be processed
with normal text editing utilities.

The paper tape punch implements these registers:

	name		size	comments

	BUF		8	last data item processed
	INT		1	interrupt pending flag
	DONE		1	device done flag
	ERR		1	error flag (PDP-9, PDP-15 only)
	POS		32	position in the output file
	TIME		24	time from I/O initiation to interrupt
	STOP_IOE	1	stop on I/O error

Error handling is as follows:

	error	     STOP_IOE	processed as

	not attached	1	report error and stop
			0	out of tape or paper

	OS I/O error	x	report error and stop

2.3.3 Terminal Input (TTI)

On the PDP-7, PDP-9, and PDP-15, the terminal interfaces (TTI, TTO)
can be set to one of three modes: KSR, 7B, or 8B.  In KSR mode, lower
case input and output characters are automatically converted to upper
case, the high order bit is forced to one on input, and printing of
ALTmode characters is supressed.  In 7B mode, input and output characters
are masked to 7 bits.  In 8B mode, characters are not modified.  Changing
the mode of either interface changes both.  The default mode is KSR.

On the PDP-9 and PDP-15, the console terminal operates, by default,
with local echo.  For backward compatibility, the terminal input can
be set to FDX (full duplex), which supresses local echo.

The terminal input (TTI) polls the console keyboard for input.  It
implements these registers:

	name		size	comments

	BUF		8	last data item processed
	INT		1	interrupt pending flag
	DONE		1	device done flag
	POS		32	number of characters input
	TIME		24	keyboard polling interval

If the simulator is debugged under Windows Visual C++, typing ^C to the
terminal input causes a fatal run-time error.  Use the following command
to simulate typing ^C:

	SET TTI CTRL-C

2.3.4 Terminal Output (TTO)

The terminal output (TTO) writes to the simulator console window.  It
implements these registers:

	name		size	comments

	BUF		8	last data item processed
	INT		1	interrupt pending flag
	DONE		1	device done flag
	POS		32	number of chararacters output
	TIME		24	time from I/O initiation to interrupt

2.3.5 Line Printers (LPT, LP9)

The line printers (LPT, LP9) write data to a disk file.  The POS
register specifies the number of the next data item to be written.
Thus, by changing POS, the user can backspace or advance the printer.

LPT is the "default" line printer for a CPU: Type 62 for the PDP-4,
Type 647 for the PDP-7 and PDP-9, and LP15 for the PDP-15.  LP9 is
the LP09 line printer controller for the PDP-9.  It may be needed
on the PDP-15 to run certain software packages.  LP9 is disabled by
default.

The Type 62 printer controller implements these registers:

	name		size	comments

	BUF		8	last data item processed
	INT		1	interrupt pending flag
	DONE		1	device done flag
	SPC		1	spacing done flag
	BPTR		6	print buffer pointer
	POS		32	position in the output file
	TIME		24	time from I/O initiation to interrupt
	STOP_IOE	1	stop on I/O error
	LBUF[0:119]	8	line buffer

The Type 647 printer controller implements these registers:

	name		size	comments

	BUF		8	last data item processed
	INT		1	interrupt pending flag
	DONE		1	device done flag
	ENABLE		1	interrupt enable (PDP-9 only)
	ERR		1	error flag
	BPTR		7	print buffer pointer
	POS		32	position in the output file
	TIME		24	time from I/O initiation to interrupt
	STOP_IOE	1	stop on I/O error
	LBUF[0:119]	8	line buffer

The LP09 printer controller implements these registers:

	name		size	comments

	BUF		7	output character
	INT		1	interrupt pending flag
	DONE		1	device done flag
	ENABLE		1	interrupt enable
	ERR		1	error flag
	POS		32	position in the output file
	TIME		24	time from I/O initiation to interrupt

The LP15 printer controller implements these registers:

	name		size	comments

	STA		18	status register
	MA		18	DMA memory address
	INT		1	interrupt pending flag
	ENABLE		1	interrupt enable
	LCNT		8	line counter
	BPTR		7	print buffer pointer
	POS		32	position in the output file
	TIME		24	time from I/O initiation to interrupt
	STOP_IOE	1	stop on I/O error
	LBUF[0:131]	8	line buffer

For all printers, error handling is as follows:

	error	     STOP_IOE	processed as

	not attached	1	report error and stop
			0	out of tape or paper

	OS I/O error	x	report error and stop

2.3.6 Real-Time Clock (CLK)

The real-time clock (CLK) frequency can be adjusted as follows:

	SET CLK 60HZ		set frequency to 60Hz
	SET CLK 50HZ		set frequency to 50Hz

The default is 60Hz.

The clock implements these registers:

	name		size	comments

	INT		1	interrupt pending flag
	DONE		1	device done flag
	ENABLE		1	clock enable
	TIME		24	clock frequency

The real-time clock autocalibrates; the clock interval is adjusted up or
down so that the clock tracks actual elapsed time.

2.3.7 Second Terminal (TTI1, TTO1)

The second terminal consists of two independent devices, TTI1 and TTO1.
The second terminal performs input and output through a Telnet session
connected to a user-specified port.  The ATTACH command specifies the
port to be used:

	ATTACH TTI1 <port>	set up listening port

where port is a decimal number between 1 and 65535 that is not being used
for other TCP/IP activities.

Once TTI1 is attached and the simulator is running, the terminal listens
for a connection on the specified port.  It assumes that the incoming
connection is a Telnet connection.  The connection remain opens until
disconnected by the Telnet client, or by a DETACH TTI1 command.

The second terminal (TTI1,TTO1) can be set to one of three modes: KSR, 7B,
or 8B.  In KSR mode, lower case input and output characters are converted
automatically to upper case, the high order bit is forced to one on input,
and printing of ALTmode characters is supressed.  In 7B mode, input and
output characters are masked to 7 bits.  In 8B mode, characters are not
modified.  Changing the mode of either device changes both.  The default
mode is KSR.

The SHOW TTI1 CONNECTIONS command displays the current connection to TTI1.
The SHOW TTI1 STATISTICS command displays statistics for the current connection.
The SET TTI1 DISCONNECT{=0} disconnects the current connection.

The second terminal input implements these registers:

	name		size	comments

	BUF		8	last data item processed
	INT		1	interrupt pending flag
	DONE		1	device done flag
	TIME		24	keyboard polling interval

The second terminal output implements these registers:

	name		size	comments

	BUF		8	last data item processed
	INT		1	interrupt pending flag
	DONE		1	device done flag
	TIME		24	time from I/O initiation to interrupt

2.4 RP15/RP02 Disk Pack (RP)

RP15 options include the ability to make units write enabled or write locked:

	SET RPn LOCKED		set unit n write locked
	SET RPn WRITEENABLED	set unit n write enabled

Units can also be set ONLINE or OFFLINE.

The RP15 implements these registers:

	name		size	comments

	STA		18	status A
	STB		18	status B
	DA		18	disk address
	MA		18	current memory address
	WC		18	word count
	INT		1	interrupt pending flag
	BUSY		1	control busy flag
	STIME		24	seek time, per cylinder
	RTIME		24	rotational delay
	STOP_IOE	1	stop on I/O error

Error handling is as follows:

	error	     STOP_IOE	processed as

	not attached	1	report error and stop
			0	disk not ready

	end of file	x	assume rest of disk is zero

	OS I/O error	x	report error and stop

2.5 Type 24 Serial Drum (DRM)

The serial drum (DRM) implements these registers:

	name		size	comments

	DA		9	drum address (sector number)
	MA		16	current memory address
	INT		1	interrupt pending flag
	DONE		1	device done flag
	ERR		1	error flag
	WLK		32	write lock switches
	TIME		24	rotational latency, per word
	STOP_IOE	1	stop on I/O error

Error handling is as follows:

	error	     STOP_IOE	processed as

	not attached	1	report error and stop
			0	disk not ready

Drum data files are buffered in memory; therefore, end of file and OS
I/O errors cannot occur.

2.6 RB09 Fixed Head Disk (RB)

The RB09 was an early fixed-head disk for the PDP-9.  It was superceded
by the RF09/RS09.  It is disabled by default.

The RB09 implements these registers:

	name		size	comments

	STA		18	status
	DA		20	current disk address
	WC		16	word count
	MA		15	memory address
	INT		1	interrupt pending flag
	WLK		20	write lock switches for track groups,
				10 tracks per group
	TIME		24	rotational delay, per word
	BURST		1	burst flag
	STOP_IOE	1	stop on I/O error

The RB09 is a data break device.  If BURST = 0, word transfers are
scheduled individually; if BURST = 1, the entire transfer occurs in
a single data break.

Error handling is as follows:

	error	     STOP_IOE	processed as

	not attached	1	report error and stop
			0	disk not ready

RB09 data files are buffered in memory; therefore, end of file and OS
I/O errors cannot occur.

2.7 RF09/RF15/RS09 Fixed Head Disk (RF)

RF09/RF15 options include the ability to set the number of platters
to a fixed value between 1 and 8, or to autosize the number of platters
from the attached file:

	SET RF 1P		one platter (256K)
	SET RF 2P		two platters (512K)
	SET RF 3P		three platters (768K)
	SET RF 4P		four platters (1024K)
	SET RF 5P		five platters (1280K)
	SET RF 6P		six platters (1536K)
	SET RF 7P		seven platters (1792K)
	SET RF 8P		eight platters (2048K)
	SET RF AUTOSIZE		autosize on attach

The default is AUTOSIZE.

The RF09/RF15 implements these registers:

	name		size	comments

	STA		18	status
	DA		21	current disk address
	WC		18	word count (in memory)
	CA		18	memory address (in memory)
	BUF		18	data buffer (diagnostic only)
	INT		1	interrupt pending flag
	WLK[0:7]	16	write lock switches for disks 0-7
	TIME		24	rotational delay, per word
	BURST		1	burst flag
	STOP_IOE	1	stop on I/O error

The RF09/RF15 is a three-cycle data break device.  If BURST = 0, word
transfers are scheduled individually; if BURST = 1, the entire transfer
occurs in a single data break.

Error handling is as follows:

	error	     STOP_IOE	processed as

	not attached	1	report error and stop
			0	disk not ready

RF15/RF09 data files are buffered in memory; therefore, end of file and OS
I/O errors cannot occur.

2.8 Type 550/555, TC02/TU55, and TC15/TU56 DECtape (DT)

The PDP-4 and PDP-7 use the Type 550 DECtape, a programmed I/O controller.
The PDP-9 uses the TC02, and the PDP-15 uses the TC15.  The TC02 and TC15
are DMA controllers and programmatically identical.  PDP-4/7 DECtape format
had 4 18b words in its block headers and trailers; PDP-9/15 DECtape format
had 5 18b words.

DECtapes drives are numbered 1-8; in the simulator, drive 8 is unit 0.
DECtape options include the ability to make units write enabled or write
locked.

	SET DTn WRITEENABLED	set unit n write enabled
	SET DTn LOCKED		set unit n write locked

Units can also be set ONLINE or OFFLINE.

The Type 550, TC02, and TC15 support PDP-8 format, PDP-11 format, and
18b format DECtape images.  ATTACH tries to determine the tape format
from the DECtape image; the user can force a particular format with
switches:

	-r			PDP-8 format
	-s			PDP-11 format
	-t			18b format

The DECtape controller is a data-only simulator; the timing and mark
track, and block header and trailer, are not stored.  Thus, the WRITE
TIMING AND MARK TRACK function is not supported; the READ ALL function
always returns the hardware standard block header and trailer; and the
WRITE ALL function dumps non-data words into the bit bucket.

The DECtape controller implements these registers:

	system	name		size	comments

	all	DTSA		12	status register A
	all	DTSB		12	status register B
	all	DTDB		18	data buffer
	all	INT		1	interrupt pending flag
	9,15	ENB		1	interrupt enable flag
	all	DTF		1	DECtape flag
	7	BEF		1	block end flag
	all	ERF		1	error flag
	9,15	CA		18	current address (memory location 30)
	9,15	WC		18	word count (memory location 31)
	all	LTIME		31	time between lines
	all	ACTIME		31	time to accelerate to full speed
	all	DCTIME		31	time to decelerate to a full stop
	all	SUBSTATE	2	read/write command substate
	all	POS[0:7]	32	position, in lines, units 0-7
	all	STATT[0:7]	18	unit state, units 0-7

It is critically important to maintain certain timing relationships
among the DECtape parameters, or the DECtape simulator will fail to
operate correctly.

	- LTIME must be at least 6
	- ACTIME must be less than DCTIME, and both need to be at
	  least 100 times LTIME

2.9 TC59/TU10 Magnetic Tape (MT)

Magnetic tape options include the ability to make units write enabled or
or write locked.

	SET MTn LOCKED		set unit n write locked
	SET MTn WRITEENABLED	set unit n write enabled

Units can also be set ONLINE or OFFLINE.

The magnetic tape controller implements these registers:

	name		size	comments

	CMD		18	command
	STA		18	main status
	CA		18	memory address (in memory)
	WC		18	word count (in memory)
	INT		1	interrupt pending flag
	STOP_IOE	1	stop on I/O error
	TIME		24	record delay
	UST[0:7]	24	unit status, units 0-7
	POS[0:7]	32	position, units 0-7

Error handling is as follows:

	error			processed as

	not attached		tape not ready; if STOP_IOE, stop

	end of file		bad tape

	OS I/O error		parity error; if STOP_IOE, stop

2.10 Symbolic Display and Input

The 18b PDP simulators implement symbolic display and input.  Display is
controlled by command line switches:

	-a			display as ASCII character
	-c			display as (sixbit) character string
	-m			display instruction mnemonics

The PDP-15 also recognizes an additional switch:

	-p			display as packed ASCII (five 7b ASCII
				characters in two 18b words)

Input parsing is controlled by the first character typed in or by command
line switches:

	' or -a			ASCII character
	" or -c			three character sixbit string
	alphabetic		instruction mnemonic
	numeric			octal number

The PDP-15 also recognizes an additional input mode:

	# or -p			five character packed ASCII string in
				two 18b words

Instruction input uses standard 18b PDP assembler syntax.  There are eight
instruction classes: memory reference, EAE, index (PDP-15 only), IOT,
operate, LAW, FP15 memory reference (PDP-15 only), and FP15 no operand
(PDP-15 only).

Memory reference instructions have the format

	PDP-4, PDP-7:	memref {I} address
	PDP-9:		memref{*} address
	PDP-15:		memref{*} address{,X}

where I (PDP-4, PDP-7) /* (PDP-9, PDP-15) signifies indirect reference,
and X signifies indexing (PDP-15 in page mode only).  The address is an
octal number in the range 0 - 017777 (PDP-4, PDP-7, PDP-9, and PDP-15 in
bank mode) or 0 - 07777 (PDP-15 in page mode).

IOT instructions consist of single mnemonics, eg, KRB, TLS.  IOT instructions
may be or'd together

	iot iot iot...

IOT's may also include the number 10, signifying clear the accumulator

	iot 10

The simulator does not check the legality of IOT combinations.  IOT's for
which there is no opcode may be specified as IOT n, where n is an octal
number in the range 0 - 07777.

EAE instructions have the format

	eae {+/- shift count}

EAE instructions may be or'd together

	eae eae eae...

The simulator does not check the legality of EAE combinations.  EAE's for
which there is no opcode may be specified as EAE n, where n is an octal
number in the range 0 - 037777.

Index instructions (PDP-15 only) have the format

	index {immediate}

The immediate, if allowed, must be in the range of -0400 to +0377.

Operate instructions have the format

	opr opr opr...

The simulator does not check the legality of the proposed combination.  The
operands for MUY and DVI must be deposited explicitly.

The LAW instruction has the format

	LAW immediate

where immediate is in the range of 0 to 017777.

FP15 memory reference instructions occupy two successive words and have
the format

	fpmem{*} address

where * signifies indirect addressing.  The address is a number in the range
0 - 0377777.

FP15 no operand instructions occupy two successive words and have the format

	fpop

The second word is ignored on output and set to 0 on input.

2.11 Character Sets

The PDP-4's console was an ASR-28 Teletype; its character encoding was
Baudot.  The PDP-4's line printer used a modified Hollerith character
set.  The PDP-7's and PDP-9's consoles were KSR-33 Teletypes; their
character sets were basically ASCII.  The PDP-7's and PDP-9's line
printers used sixbit encoding (ASCII codes 040 - 0137 masked to six
bits).  The PDP-15's I/O devices were all ASCII.  The following table
provides equivalences between ASCII characters and the PDP-4's I/O devices.
In the console table, FG stands for figures (upper case).

		 PDP-4			   PDP-4
ASCII		console	 		line printer

000 - 006	none			none
bell		FG+024			none
010 - 011	none			none
lf		010			none
013 - 014	none			none
cr		002			none
016 - 037	none			none
space		004	     		000
!		FG+026			none
"		FG+021			none
#		FG+005			none
$		FG+062			none
%		none			none
&		FG+013			none
'		FG+032			none
(		FG+036			057
)		FG+011			055
*		none			072
+		none			074
,		FG+006			033
-		FG+030			054
.		FG+007			073
/		FG+027			021
0		FG+015			020
1		FG+035			001
2		FG+031			002
3		FG+020			003
4		FG+012			004
5		FG+001			005
6		FG+025			006
7		FG+034			007
8		FG+014			010
9		FG+003			011
:		FG+016			none
;		FG+017			none
<		none			034
=		none			053
>		none			034
?		FG+023			037
@		none			{MID DOT} 040
A		030			061
B		023			062
C		016			063
D		022			064
E		020			065
F		026			066
G		013			067
H		005			070
I		014			071
J		032			041
K		036			042
L		011			043
M		007			044
N		006			045
O		003			046
P		015			047
Q		035			050
R		012			051
S		024			022
T		001			023
U		034			024
V		017			025
W		031			026
X		027			027
Y		025			030
Z		021			031
[		none			none
\		none			{OVERLINE} 056
]		none			none
^		none			{UP ARROW} 035
_		none			UC+040
0140 - 0177	none			none
