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Power-On and Reset Auto-Jump
The front panel can force an auto-jump upon power-on and/or reset. The auto-jump address can be dif-
ferent for power-on than for reset. This is unlike many auto-jump circuits which perform the same ac-
tion for power-on and for reset. For Altair BASIC and Altair DOS, duplicate auto-jump addresses can be
problematic. For example, the RESET switch is normally used to regain control from an executing or
hung program and return to the BASIC or DOS prompt. However, if the RESET switch instead forces an
auto-jump to the cold boot code in PROM, then the entire initialization process for BASIC or DOS – in-
cluding the slow process of mounting each disk – must be performed. For these programs, it is best to
have a power-on auto-jump without a reset auto-jump.
Power-On Auto-Jump
The MSB of the power-on auto-jump address is specified on VDIP #2. If a non-zero value is specified,
then upon power-on, the front panel forces a clean reset, an “examine” of the auto-jump address, and
then lets the 8080 processor run. If a value of zero is specified, power-on auto-jump is disabled.
Reset Auto-Jump
Whenever RESET is released, the front panel can force an “examine” of an address you specify. This sets
the 8080 program counter to this address and therefore performs an auto-jump to the specified address
if the computer is running. Note that if the computer is not running when RESET is actuated (or a
STOP/RESET is performed), this has the effect of examining the auto-jump address upon reset with the
computer remaining in a stopped state.
The MSB of the reset auto-jump address is specified on VDIP #3. If a value of zero is specified, the reset
auto-jump is disabled.
Updating Virtual DIP Switches
The virtual DIP switch (VDIP) values are stored in EEPROM. The VDIP values can be examined and updat-
ed from the front panel. The AUX-Right switch is used like the “Ctrl” key on a keyboard to give each
front panel switch an additional function. While holding AUX-Right in the UP position, the front panel
switches provide the following functions when actuated:
EXAMINE
(with AUX-Right held up) places the value of VDIPs 1-3 into Altair RAM locations 1-3. The
firmware version is placed into RAM location zero. This allows you to “examine” the virtual DIP
switch values.
DEPOSIT
(with AUX-Right held up) “deposits” the values from Altair memory locations 1-3 into VDIPs
1-3 in EEPROM.
RESET
(with AUX-Right held up) resets the front panel into safe mode. See the “Firmware Updates”
section for more information about safe mode.
Once VDIP values are placed into Altair RAM using AUX-Right/EXAMINE, the values can be viewed and
changed in Altair memory using normal front panel examine and deposit operations. Once the VDIP val-
ues are as you want them, write them back to EEPROM using the AUX-Right/DEPOSIT sequence.
