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← Expansion Region 2 Access Width

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---
title: Expansion Region 2 Access Width
type: test
summary: Reads and writes expansion region 2 at every width under two bus width settings.
category: Hardware tests
info: Machine = SCPH-5501
info: Program = exp2-width (pcsx-redux nugget)
---

## Overview

The program reads 1F802000h in [expansion region 2](/hardware/expansion-port/) with LB, LH and LW, and writes 1F802040h and 1F802041h with SB, SH and SW. It prints a line before and after each access, so a hang shows as a BEFORE line with no AFTER line. It runs the whole set once with the EXP2 delay/size register (1F80101Ch) at its value on entry and once with the register set for a 16-bit bus.[^src]

## Results

Every access completed under both settings. No access raised an exception or hung the console. The register read 00080777h on entry. Reads of 1F802000h returned FFh, FFFFh and FFFFFFFFh for the three widths, which is the value of an empty bus on a retail board.[^out]

## Runs

### 22 October 2026 link-3

Raw output: [EXP2WIDTH.txt](/tests/raw/20261022T2245Z-5501a-link-3/exp2width/EXP2WIDTH.txt) · [bench.txt](/tests/raw/20261022T2245Z-5501a-link-3/exp2width/bench.txt)

EXP2WIDTH.txt:

```
EXP2W-START dev8=00080777
bios BEFORE lb
bios AFTER lb ff
bios BEFORE lh
bios AFTER lh ffff
bios BEFORE lw
bios AFTER lw ffffffff
bios BEFORE sb
bios AFTER sb
bios BEFORE sh
bios AFTER sh
bios BEFORE sw
bios AFTER sw
w16 BEFORE lb
w16 AFTER lb ff
w16 BEFORE lh
w16 AFTER lh ffff
w16 BEFORE lw
w16 AFTER lw ffffffff
w16 BEFORE sb
w16 AFTER sb
w16 BEFORE sh
w16 AFTER sh
w16 BEFORE sw
w16 AFTER sw
EXP2W-DONE
ResetGraph:jtb=801e78b8,env=801e7900
```

bench.txt:

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

## References

[^src]: pcsx-redux nugget, tests/exp2-width/exp2-width.c, header comment. MIT License. https://github.com/pcsx-redux/nugget
[^out]: Hardware test run 20261022T2245Z-5501a-link-3: [exp2width/EXP2WIDTH.txt](/tests/raw/20261022T2245Z-5501a-link-3/exp2width/EXP2WIDTH.txt).