VAXstation 100 firmware notes

Some random notes from running the DEC-supplied standard firmware for the VAXstation 100 in an emulator.

The firmware analyzed announces itself as version 05.00. It deviates in minor details from the information in the 1983 "VS100 Engineering Specification".

Memory map

Firmware 5.00 extends the LOOPBACK region to one more word at 4A0004. Apparently this loops back the value written to 480004. It also accesses a byte at 280000, seemingly to clear a BBA interrupt.

Error LEDs

Indicates which test failed. During power-up, green light turned off. During idle loop, green light remains on.

Apparently there's a bug.

Interrupts

All VS100 interrupts use the autovector feature.

Firmware 5.00 doesn't use the level 1 interrupt. The firmware only reads the mouse position during maintenance test.

Keyboard test

The firmware transmits code FD (hex) to the LK201 keyboard, which commands it to jump to the power-up sequence and self-test. The keyboard transmits a four-byte message back. The VS100 ignores the keyboard ID, and checks that the third is not 3D.

This information is from the VT220 Technical Manual.

D0 flags

The firmware maintains a set of flags in register D0.

Bit (decimal)	Meaning
16	Manufacturing mode.
17	BBA present.
18	Link down.
19	Power-up error.
20	LEDs locked.
21	Suppress printing test result.
22	In maintenance menu.
23	Keyboard ok.
24	BBA done.
25	Vertical retrace interrupt.
26	Test not executed. (E.g. hardware not present.)
27	Test timed out.
28	TRAP #1