To:	Users
From:	Bob Supnik
Subj:	IBM 1401 Simulator Usage
Date:	15-Jan-2002

			COPYRIGHT NOTICE

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

   Original code published in 1993-2002, written by Robert M Supnik
   Copyright (c) 1993-2002, 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 IBM 1401 simulator.


1. Simulator Files

sim/		sim_defs.h
		scp.c
		scp_tty.c
		sim_rev.c

sim/i1401/	i1401_defs.h
		i1401_cpu.c
		i1401_iq.c
		i1401_lp.c
		i1401_mt.c
		i1401_sys.c	

2. IBM 1401 Features

The IBM 1401 simulator is configured as follows:

device		simulates
name(s)

CPU		IBM 1401 CPU with 16K of memory
CDR,CDP		IBM 1402 card reader/punch
LPT		IBM 1403 line printer
INQ		IBM 1407 inquiry terminal
MT		IBM 729 7-track magnetic tape controller with six drives

The IBM 1401 simulator implements many unique stop conditions.  On almost
any kind of error the simulator stops:

	unimplemented opcode
	reference to non-existent memory
	reference to non-existent device
	no word mark under opcode
	invalid A address
	invalid B address
	invalid instruction length
	invalid modifier character
	invalid branch address
	invalid magtape unit number
	invalid magtape record length
	write to locked magtape drive
	skip to unpunched carriage control tape channel
	card reader hopper empty
	address register wrap-around
	single character A field in MCE
	single character B field in MCE
	hanging $ in MCE with EPE enabled
	I/O check with I/O stop switch set

The LOAD and DUMP commands are not implemented.

2.1 CPU

The CPU options include a number of special features and the size of main
memory.  Note that the Modify Address special feature is always included
when memory size is greater than 4K.

	SET CPU XSA		enable advanced programming special feature
	SET CPU NOXSA		disable advanced programming
	SET CPU HLE		enable high/low/equal special feature
	SET CPU NOHLE		disable high/low/equal
	SET CPU BBE		enable branch on bit equal special feature
	SET CPU NOBBE		disable branch on bit equal
	SET CPU MR		enable move record special feature
	SET CPU NOMR		disable move record
	SET CPU EPE		enable extended print edit special feature
	SET CPU NOEPE		disable extended print edit
	SET CPU 4K		set memory size = 4K
	SET CPU 8K		set memory size = 8K
	SET CPU 12K		set memory size = 12K
	SET CPU 16K		set memory size = 16K

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.  Initially, memory size is 16K, and all special
features are enabled.

Memory is implemented as 7 bit BCD characters, as follows:

	6	5 	4	3	2	1	0

	word	B bit	A bit	8	4	2	1
	mark	<-- zone -->	<-------- digit -------->

In BCD, the decimal digits 0-9 are (octal) values 012, 001, 002, 003, 004,
005, 006, 007, 010, 011, respectively.  Signs are encoded in the zone bits,
with 00, 01, and 11 being positive, and 10 being negative.

CPU registers include the visible state of the processor.  The 1401 has no
interrupt system.

	name		size	comments

	IS		14	instruction storage address register (PC)
	AS		14	A storage address register
	BS		14	B storage address register
	ASERR		1	AS invalid flag
	BSERR		1	BS invalid flag
	SSA		1	sense switch A
	SSB		1	sense switch B
	SSC		1	sense switch C
	SSD		1	sense switch D
	SSE		1	sense switch E
	SSF		1	sense switch F
	SSG		1	sense switch G
	EQU		1	equal compare indicator
	UNEQ		1	unequal compare indicator
	HIGH		1	high compare indicator
	LOW		1	low compare indicator
	OVF		1	overflow indicator
	IOCHK		1	I/O check switch
	PRCHK		1	process check switch
	ISQ		1	IS prior to last branch;
				most recent IS change first
	WRU		8	interrupt character

2.2 1402 Card Reader/Punch (CDR, CDP, STKR)

The IBM 1402 card/reader punch is simulated as three independent devices:
the card reader (CDR), the card punch (CDP), and the reader and punch
stackers (STKR).  STRK units 0, 1, 2, and 4 correspond to the reader
normal stacker, reader stacker 1, shared stacker 2/8, and punch stacker
4, respectively.

The card reader supports the BOOT command.  BOOT CDR reads a card image
into locations 1-80, sets a word mark under location 1, clears storage,
and then transfers control to location 1.

The card reader reads data from disk files, while the punch and stackers
write data to disk files.  Cards are simulated as ASCII text lines with
terminating newlines; column binary is not supported.  For each unit,
the POS register specifies the number of the next data item to be read or
written.  Thus, by changing POS, the user can backspace or advance these
devices.

The reader/punch registers are:

	device	name		size	comments

	CDR	LAST		1	last card indicator
		ERR		1	error indicator
		S1		1	stacker 1 select flag
		S2		1	stacker 2 select flag
		POS		31	position
		TIME		24	delay window for stacker select
		BUF[0:79]	8	reader buffer

	CDP	ERR		1	error indicator
		S4		1	stacker 4 select flag
		S8		1	stacker 8 select flag

	STKR	POS0		31	position, normal reader stack
		POS1		31	position, reader stacker 1
		POS2		31	position, shared stacker 2/8
		POS4		31	position, punch stacker 4

Error handling is as follows:

	device		error		processed as

	reader		end of file	if SSA set, set LAST indicator
					on next Read, report error and stop

	reader,punch	not attached	report error and stop
			OS I/O error	print error message
					if IOCHK set, report error and stop
					otherwise, set ERR indicator

	stacker		not attached	ignored
			OS I/O error	print error message
					if IOCHK set, report error and stop

2.3 1403 Line Printer (LPT)

The IBM 1403 line printer (LPT) writes its data, converted to ASCII, to
a disk file.  The line printer supports three different print character
sets or "chains":

	SET LPT PCF			full 64 character chain
	SET LPT PCA			48 character business chain
	SET LPT PCH			48 character FORTRAN chain

In addition, the line printer can be programmed with a carriage control
tape.  The LOAD command loads a new carriage control tape:

	LOAD <file>			load carriage control tape file

The format of a carriage control tape consists of multiple lines.  Each
line contains an optional repeat count, enclosed in parentheses, optionally
followed by a series of column numbers separated by commas.  Column numbers
must be between 1 and 12; a column number of zero denotes top of form.  The
following are all legal carriage control specifications:

	<blank line>			no punch
	(5)				5 lines with no punches
	1,5,7,8				columns 1, 5, 7, 8 punched
	(10)2				10 lines with column 2 punched
	1,0				column 1 punched; top of form

The default form is 66 lines long, with column 1 and the top of form mark
on line 1, and the rest blank.

The line printer registers are:

	name		size	comments

	LINES		8	number of newlines after next print
	LFLAG		1	carriage control flag (1 = skip, 0 = space)
	CCTP		8	carriage control tape pointer
	CCTL		8	carriage control tape length (read only)
	ERR		1	error indicator
	POS		31	position
	CCT[0:131]	32	carriage control tape array	

Error handling is as follows:

	error			processed as

	not attached		report error and stop

	OS I/O error		print error message
				if IOCHK set, report error and stop
				otherwise, set ERR indicator

2.4 1407 Inquiry Terminal (INQ)

The IBM 1407 inquiry terminal (INQ) is a half-duplex console.  It polls
the console keyboard periodically for inquiry requests.  The inquiry
terminal registers are:

	name		size	comments

	INQC		7	inquiry request character (initially ESC)
	INR		1	inquiry request indicator
	INC		1	inquiry cleared indicator
	TIME		24	polling interval

When the 1401 CPU requests input from the keyboard, the message [Enter]
is printed out, followed by a new line.  The CPU hangs waiting for input
until either the return/enter key is pressed, or the inquiry request
character is typed in.  The latter cancels the type-in and sets INC.

The inquiry terminal has no errors.

2.5 729 Magnetic Tape (MT)

The magnetic tape controller supports six drives, numbered 1 through 6.
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 simulator
supports the BOOT command.  BOOT MT reads the first record off tape,
starting at location 1, and then branches to it. 

The magnetic tape controller implements these registers:

	name		size	comments

	END		1	end of file indicator
	ERR		1	error indicator
	PAR		1	parity error indicator
	POS1..6		31	position, drives 1..6

Error handling is as follows:

	error			processed as

	not attached		report error and stop

	end of file		(read or space) end of physical tape
				(write) ignored

	OS I/O error		print error message
				if IOCHK set, report error and stop
				otherwise, set ERR indicator

2.6 Symbolic Display and Input

The IBM 1401 simulator implements symbolic display and input.  Display is
controlled by command line switches:

	-c			display as single character
				(BCD for CPU and MT, ASCII for others)
	-s			display as wordmark terminated BCD string
				(CPU only)
	-m			display instruction mnemonics
				(CPU only)

In a CPU character display, word marks are denoted by ~.

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

	' or " or -c or -s	characters (BCD for CPU and MT, ASCII
				for others)
	alphabetic		instruction mnemonic
	numeric			octal number

Instruction input is free format, with spaces separating fields.  There
are six instruction formats: 1, 2, 4, 5, 7, and 8 characters:

	1 character		opcode
	2 character		opcode 'modifier
	4 character		opcode address
	5 character		opcode address 'modifier
	7 character		opcode address address
	8 character		opcode address address 'modifier

Addresses are always decimal, except for special I/O addresses in the A
field, which may be specified as %xy, where x denotes the device and y
the unit number.

For the CPU, string input may encompass multiple characters.  A word mark
is denoted by ~ and must precede the character to be marked.  All other
devices can only accept single character input, without word marks.

2.7 Character Sets

The IBM 1401 used a 6b character code called BCD (binary coded decimal).
Some of the characters have no equivalent in ASCII and require different
representations:

BCD	    ASCII	IBM 1401		print
code	representation	character		chains

00	space
01	1
02	2
03	3
04	4
05	5
06	6
07	7
10	8
11	9
12	0
13	#					= in H chain
14	@					' in H chain
15	:					blank in A, H chains
16	>					blank in A, H chains
17	(		tape mark		blank in A, H chains
20	^		alternate blank		blank in A, H chains
21	/
22	S
23	T
24	U
25	V
26	W
27	X
30	Y
31	Z
32	'		record mark
33	,
34	%					( in H chain
35	=		word mark		blank in A, H chains
36	\					blank in A, H chains
37	+					blank in A, H chains
40	-
41	J
42	K
43	L
44	M
45	N
46	O
47	P
50	Q
51	R
52	!
53	$
54	*
55	]					blank in A, H chains
56	;					blank in A, H chains
57	_		delta			blank in A, H chains
60	&
61	A
62	B
63	C
64	D
65	E
66	F
67	G
70	H
71	I
72	?
73	.
74	)		lozenge
75	[					blank in A, H chains
76	<					blank in A, H chains
77	"		group mark		blank in A, H chains
