Using the Tape Drive on the Simulator
Inserting/Removing a Cassette
The "Release" button (eject cassette on the Wang 700) will pop-up a
file select dialog and allow you to select a file to use as a "tape
cassette". An existing file may be used, although note that proper
positioning is required unless you intend to overwrite the contents. If a
new file name is typed in the dialog, then that file is created, empty.
Clicking Release followed by Cancel (in the dialog window) will make
the tape drive "empty", as if it had no cassette. Attempting to press
"Ready" will fail, and attempts to load or record to the tape will hang
with a blank display.
Positioning the Tape
The "Forward" and "Rewind" buttons will position the tape forward, or backward,
by "records". Each "record" on the tape is marked with a special code to
indicate internally that the recorded image ends. Note how this differs
from the Wang 700 tape unit, where precise positioning using Forward and Reverse
was difficult at best, if not impossible, due to the guesswork of where the
tape records ended.
Note, there was a trick that can be used to manage the
tape position. If the P.C. is set near the end of the range, and a program loaded,
only the last 16 program steps will be overwritten.
As long as no data or program steps in that range
need to be preserved, multiple programs on one tape can be skipped.
Simulator Details Note:
The tape "record marks" in the file are two bytes, the first being 0x5c
(END PROG) and the second being either 0x5c (if it represents
a real END PROG) or 0xff in case the tape was simply stopped
without recording an END PROG code. The rest of the bytes in the
file directly correspond to data, either program steps or digit-pairs
Making the Tape Ready for Operations
In order to record to, and load from, a tape the "Tape Ready" button must
be depressed. This is the only button on the tape unit that toggles. All
others are "momentary operation". Pressing any of the buttons on the
tape when Ready is engaged will release the Ready button, making the
tape unit "not ready". This is especially noticeable when using the tape
Loading a Program
When the tape positioned as desired (typically at "record 0") and the "Tape Ready"
button depressed, click the LOAD PROG button. The display will blank momentarily
(depending on the length of the program) and then come back on. The tape
position indicator should have advanced.
Verifying a Loaded Program
Pressing the VERIFY PROG button will execute a "check sum" of all program
codes (except the END PROG) and display that sum.
This number can be compared to a known
result to confirm that the program is properly loaded and is ready to run.