The 4002 is the data/IO partner of the 4004/4040. 16-pin DIP, 80
nibbles (4 registers × 16 main chars + 4 status chars each), plus
4 dedicated output port pins driven by the WMP instruction.
This skeleton:
- Pin contract registered (D0..D3, O0..O3, SYNC, CL, RESET, CM,
VDD, VSS).
- Storage allocated (main[4][16] + status[4][4] arrays).
- SYNC + own timer + CM-strobe gating tracks the SRC chip-select
latch at X2/X3 (compile-time RAM4002_CHIP_PAIR selects which of
4 chip pairs this instance responds to).
- RESET clears storage and drops output port to 0.
Not yet implemented (Phase D-2 follow-up): full SRC + WRM/RDM/WR0..3/
RD0..3 round-trip with the 4004. The 4004 chip currently stubs
those I/O instructions, so even though the 4002's address-latching
works, no data ever flows. Requires modifying 4004.c to drive the
bus during X2/X3 of SRC and during M2 of the I/O group.
Tests: 2/2 passing (pin contract + RESET behaviour). Total
test_intel: 111→113 passing. The 4-chip 4004 ecosystem (4001 +
4002 + 4004 + canvas-deployable variants) now exists.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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