INSTALLING THE SIC SIMULATOR
The SIC simulator is written in standard Pascal. It should
be possible to install this simulator on almost any computer with
a Pascal compiler, by making the minor changes described below.
MAIN MEMORY SIZE
The largest address in the simulated memory is hexadecimal 2FFF
(decimal 12287). This memory size can be changed by changing the
value of the constant msize (line 34).
SIC FEATURES
This version of the simulator supports most SIC/XE instructions and
features (see the user documentation for details). For a simulator
that supports only standard SIC features, set the constant xe (line
35)
to false.
CHARACTER CODES
The simulated SIC machine uses ASCII character codes. In order to
perform I/O operations, the simulator must translate between ASCII
and the character codes being used by the host machine. The
information needed to do this translation is supplied in the arrays
intab and outtab; initialization statements for the values in
these arrays begin at line 1746.
If the host machine uses ASCII character codes, the only
initialization needed is the statement
for i := 0 to 255 do
intab[i] := i;
If the host machine uses a different set of character codes,
initialization is performed with a series of statements of the
form
intab[h] := a;
where 'h' is the ordinal value for some character on the host
computer, and 'a' is the ordinal value for the same character in
the ASCII character set. Following this sequence should be the
statement
for i := 0 to 255 do
outtab[i] := c;
where 'c' is the ordinal value for a period on the host machine.
(This causes ASCII characters which are not available in the
character set of the host machine to be translated as '.').
INPUT AND OUTPUT
All of the assign statements are located in the procedure
initialize (lines 1734-1741). These statements may need to be
changed (or removed) if your system uses some other means for
associating internal and external file names. Similarly, the
close statements (lines 831, 1855-1860) may need to be changed
or removed.
Standard Pascal I/O procedures for text files do not provide
satisfactory support for interactive input. The basic problem is
that an automatic reset operation is performed on file input when
the program begins execution. This reset may attempt to read the
first line from input, which causes the program to ask the user
for input before the first prompt message has been written out.
Most compilers make some special provision for interactive
files; however, the details vary from one system to another.
If commands and responses seem out of order, you may need to seek
assistance from someone who is familiar with interactive input
on your system. Fortunately, this is a common problem, so the
solution should not be difficult to locate. The only readln for
file input is contained in the procedure readl. This procedure
is called by the main program (line 1837). All reading of data
from input is done by procedure readc, which reads a single
character for each call.
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HOW TO USE THE SIC SIMULATOR
After initializing, the simulator will display
SIC SIMULATOR V1.6
COMMAND: S(tart, R(un, E(nter, D(ump, H(count, B(kpt,
Q(uit ?
You may now enter any of the commands described below; each
command may be abbreviated by entering only its first letter.
Commands and other alphabetic characters (such as hexadecimal
digits) may be entered using either lowercase or uppercase letters.
START
Entering S causes the simulator to read 128 bytes of data from
device 00 into memory, starting at address 0000. This command
would normally be used to bootstrap a loader or other program
into memory. See the description of I/O device conventions
below for further information.
RUN
This command causes the simulator to begin executing SIC
machine language instructions from a program in memory. There
are two forms of the command:
R
R address
If an address is specified in the command, the next instruction
to be executed is the one starting at that address. (All
addresses specified in commands are given in hexadecimal.) If
no address is specified, the next instruction to be executed is
the one following the last previously-executed instruction, if
any, or the instruction beginning at address 0000.
Execution continues until an error occurs, or the number of
instructions specified by HCOUNT have been executed, or a
breakpoint specified by BKPT is reached (see below).
ENTER
This command is used to enter values into registers or memory
locations. The two possible forms of the command are
E Rn xxxxxx
E address xxxx...
In the first case, Rn is a register identifier (RA, RX, RL,
etc.). Data to be entered into the register is given in
hexadecimal notation, with two hexadecimal digits specifying
each byte of data. When entering data into a register, exactly
three bytes (6 hex digits) must be given.
In the second case, any number of bytes of data may be entered
into memory, starting at the address specified. Each byte of
data to be entered is specified with two hexadecimal digits, as
above.
DUMP
This command is used to display the contents of registers and
memory locations. There are three possible forms of the
command:
D R
D startaddr-endaddr
D R,startaddr-endaddr
If R is specified, the contents of all registers are displayed
in hexadecimal, along with the current value of the condition
code. If startaddr and endaddr are specified, the contents of
the indicated range of addresses are displayed; a maximum of
320 (decimal) bytes can be dumped at one time. Because memory
is displayed in rows of 16 bytes each, the actual dump may
include some bytes before startaddr and some bytes after
endaddr.
HCOUNT
This command is used to specify the maximum number of SIC
instructions to be executed in response to a RUN command. This
limit allows the user to regain control in case of an unending
loop in the program being simulated. The command has the form
H n
where n is a value given by 1 to 4 decimal digits. The
maximum value that can be specified is 9999; if no HCOUNT
command is entered, the default value is 1000.
After n instructions have been executed, the simulator displays
n INSTRUCTIONS EXECUTED
P=xxxxxx
where xxxxxx is the current program counter value (i.e., the
address of the next instruction to be executed). Entering
RUN as the next command will resume execution at this point
(for another n instructions).
BKPT
This command is used to set a breakpoint to control instruction
execution. The form of the command is
B address
When the next instruction to be executed begins at the
specified address, the simulator displays
BREAKPOINT REACHED
P=xxxxxx
where xxxxxx is the current location counter value (i.e., the
breakpoint address). Entering RUN as the next command will
resume execution at this point.
QUIT
This command is used to terminate the simulation.
I/O DEVICE CONVENTIONS
Device 00 (file name DEV00) is used only by the START command;
it contains 128 bytes of bootstrap data, represented with two
hexadecimal digits (characters 0-9 and A-F) per byte. For ease
of creation and editing, this file is represented as a text
file with four lines of data; each line contains 64 characters
(which represent 32 bytes of data).
The simulator currently supports six simulated SIC devices for
use by the program: devices F1, F2, and F3 (file names DEVF1,
DEVF2, and DEVF3), which can be used only for input, and
devices 04, 05, and 06 (file names DEV04, DEV05, and DEV06),
which can be used only for output. On any of these files,
each byte of data is represented as one character. The files
may contain any character which is part of the character set of
the host machine; translation between the host machine's
character set and ASCII is handled by the simulator. On input,
an end-of-line is read as hexadecimal 00; an end-of-file is
read as hexadecimal 04. On output, writing a hexadecimal 00
causes an end-of-line to be inserted.
Device timing delays are simulated via the TD instruction.
Except for the first time the device is addressed, a TD issued
to a device will return the "device busy" indication from 1 to
4 times before signalling "device ready". An attempt to
execute an RD or WD instruction before the device is ready will
cause an error message.
NOTES
1. The largest main memory address is 2FFF. When the simulator
is initialized, all registers are set to FFFFFF and all
memory locations are set to FF.
2. The file LOG contains a listing of all terminal input and
output for the simulation run. This file may be printed
to obtain a hard-copy record of the simulation.
3. When the simulator detects a run-time error (for example,
illegal machine instruction, address out of range, or
arithmetic overflow) it displays an
current program counter value. This
the address of the instruction that
the address of the next instruction
upon the type of error detected).
error message and the
value will be either
caused the error, or
following it (depending
LIMITATIONS
This version of the SIC simulator supports all SIC/XE instructions
and features except for the following:
1. Floating-point data type and instructions (ADDF, COMPF, DIVF,
FIX, FLOAT, LDF, MULF, NORM, STF, SUBF)
2. I/O channels and associated instructions (SIO, TIO, HIO)
3. Interrupts and associated instructions (LPS, STI, SVC)
4. Register SW and associated features (user/supervisor modes,
running/idle states)
5. Memory protection and associated instructions (SSK)