64 lines
2.0 KiB
Markdown
64 lines
2.0 KiB
Markdown
# test_4040 — Intel 4040 as a velxio custom chip
|
|
|
|
See [../autosearch/02_intel_chips_overview.md](../autosearch/02_intel_chips_overview.md#intel-4040-1974)
|
|
for the spec.
|
|
|
|
## Status
|
|
|
|
📋 **Spec only.** Will reuse the 4004 emulator core once that's
|
|
working.
|
|
|
|
## Pin contract (24-pin DIP, real silicon)
|
|
|
|
The 4040 is a 4004 superset; it keeps every 4004 signal and adds:
|
|
|
|
- `INT` (interrupt request, in)
|
|
- `STOP` (single-step, in)
|
|
- `STOP ACK` (out)
|
|
- Additional bank-select / index-pointer lines
|
|
|
|
**Action item:** pull the exact 4040 pinout from a datasheet and fill
|
|
in this table before writing `.chip.json`. Pin order matters for the
|
|
on-canvas drag-and-drop appearance.
|
|
|
|
| Pin | Name | Dir | Notes |
|
|
| --- | --------- | ----- | ----- |
|
|
| | D0..D3 | I/O | Same multiplexed nibble bus as 4004 |
|
|
| | CLK1, CLK2| in | |
|
|
| | SYNC | out | |
|
|
| | RESET | in | |
|
|
| | TEST | in | |
|
|
| | CM-ROM0..1| out | 4040 has *two* ROM strobes (4004 has one) |
|
|
| | CM-RAM0..3| out | |
|
|
| | INT | in | New on 4040 |
|
|
| | STOP | in | New on 4040 |
|
|
| | STOP ACK | out | New on 4040 |
|
|
| | VDD, VSS | power | |
|
|
|
|
## Implementation plan
|
|
|
|
1. Land the 4004 first.
|
|
2. Fork its `.c` source into `4040.c`.
|
|
3. Extend the register file from 16 → 24 4-bit registers.
|
|
4. Extend the PC stack from 3-deep → 7-deep.
|
|
5. Add the new opcodes (interrupt enable/disable, return-from-interrupt,
|
|
stop, the extra register-pair operations).
|
|
6. Add `INT` pin watch. On rising edge, push PC and vector to fixed
|
|
address `[verify from datasheet]`.
|
|
7. Add `STOP` pin watch. On rising edge, freeze the cycle timer and
|
|
assert `STOP ACK`.
|
|
|
|
## Target demo sketch
|
|
|
|
Same as 4004 (LED blink), then a second sketch that uses `INT` —
|
|
an external "button" chip drives `INT`, the 4040's ISR toggles a
|
|
different output. Demonstrates the only feature that matters versus
|
|
the 4004.
|
|
|
|
## Files to create later
|
|
|
|
- `4040.chip.json`
|
|
- `4040.c`
|
|
- `sketch_blink.asm`
|
|
- `sketch_irq.asm`
|