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into memory, the checksum loader then reads in BASIC from the remainder of
the cassette tape.
The code for the bootstrap loader is provided by Altair in the BASIC manual.
Different versions of the bootstrap loader are required based on the version
of BASIC and the type of interface card being used to load BASIC. For this
demonstration, we need the bootstrap loader for the 88-ACR cassette interface
and for 8K BASIC Version 4.0. Following is the bootstrap loader code for this
combination of BASIC and serial port type:
Addr Data
---- ----
Addr Data
---- ----
Addr Data
---- ----
000 041
001 302
002 037
003 061
004 022
005 000
006 333
007 006
010 017
011 330
012 333
013 007
014 275
015 310
016 055
017 167
020 300
021 351
022 003
023 000
Follow these steps to enter the bootstrap loader:
1) Turn the power switch on.
2) Raise and hold the STOP switch in the STOP position, then raise and re-
lease the RESET switch. Finally, release the STOP switch. This performs
a hard reset on the computer and sets all address lights to zero.
3) Put the first data byte in switches 7 through 0, then raise DEPOSIT.
4) Put the data for the next address in switches 7 through 0, then depress
DEPOSIT NEXT.
5) Repeat step 4 until all bytes have been entered.
6) Raise and release RESET to force all address lights back to zero.
7) Verify the data shown on lights D7 through D0 matches the data byte for
the current address. If the value is correct, go to step 9, otherwise
go to step 8.
8) Put the correct value in switches 7 through 0, then raise DEPOSIT.
9) Depress EXAMINE NEXT
10) Repeat steps 7 through 9 to validate entry of the entire program.
Once the bootstrap loader is entered and verified, we’re almost ready to load
BASIC. But first, we must set the run address to zero and then set the front
panel sense switches to tell the checksum loader and BASIC the type of serial
ports in use for the console device and for the load device:
1) Set all address switches to zero.
2) Raise EXAMINE to set all address lights (and the 8080 program counter)
to zero.
3) Raise A12 to the up position. This tells the checksum loader and BASIC
that a 2SIO serial board with one stop bit is the console interface.
4) Raise A9 and A8 to the up position. This tells the checksum loader that
the cassette interface is being used to load BASIC.
Now we’re finally ready to actually load BASIC!
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