The display has a third use: serial error annunciator. $D5F2 renders
'E0' + three live counters (TX-ring overflow $3187, reply retries
$3184, give-up teardowns $3185); $DAB8/$DAB2 is a terminal crash
screen spelling 'dEAd' when the TX dispatcher meets an unknown command
byte. Also recorded: RX overrun is unhandled (checksum NAKs are the only
symptom), unused vectors hang in BRA-self stubs, FAULT LED = MAX690 PFO,
manual/remote reset works by pulling PFI low, RUN LED = buffered AS*,
and the MAX690 watchdog is unconnected/unserviced — software wedges
persist until reset, matching bench observations.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
New display-board-1408.md: pin-level definition of the board's outputs
(8 multiplexed hex digits via ICM7228B, isolated LPT LED monitor block,
no readback path) and, from the firmware disassembly, everything the RIO
puts on it: F0 boot banner, F1 test-mode banner (keypad sequence A-9-E
enters, D exits), and the sub-test displays — five live encoder-count
readouts, button test with input index, two lamp patterns, keypad test.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
CydandClaude Fable 5