View source for EXP2 Delay Register Read-back

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---
title: EXP2 Delay Register Read-back
type: test
summary: Writes the expansion region 2 delay/size register with four values and reads each back.
category: Hardware tests
info: Machine = SCPH-5501
info: Program = dev8-readback (pcsx-redux nugget)
---

## Overview

The program writes the EXP2 delay/size register at 1F80101Ch, the register for [expansion region 2](/hardware/expansion-port/) (DEV8), with four values and reads each back twice. It then puts back the value the register held on entry.[^out]

## Results

The register held 00080777h on entry. Each value written read back unchanged on both reads: 00070777h, 00080777h, 00000777h and 00010777h, so bits 16 to 19 of the register keep any value written. The register read 00080777h again after it was put back.[^out]

## Runs

### 22 October 2026 link-2

Raw output: [DEV8READBACK.txt](/tests/raw/20261022T2245Z-5501a-link-2/dev8readback/DEV8READBACK.txt) · [bench.txt](/tests/raw/20261022T2245Z-5501a-link-2/dev8readback/bench.txt)

DEV8READBACK.txt:

```
D8RB entry=00080777
D8RB wrote=00070777 read=00070777 00070777
D8RB wrote=00080777 read=00080777 00080777
D8RB wrote=00000777 read=00000777 00000777
D8RB wrote=00010777 read=00010777 00010777
D8RB-DONE restored=00080777
ResetGraph:jtb=801e78b8,env=801e7900
```

bench.txt:

```
257 bytes of TTY text in psx.log
```

## References

[^out]: Hardware test run 20261022T2245Z-5501a-link-2: [dev8readback/DEV8READBACK.txt](/tests/raw/20261022T2245Z-5501a-link-2/dev8readback/DEV8READBACK.txt). The program is nugget's tests/dev8-readback, https://github.com/pcsx-redux/nugget