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MBC7: Note about HALT and sensor relying on PHI/ cart clock #596

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MBC7: Note about HALT and sensor relying on PHI/ cart clock #596

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8 changes: 7 additions & 1 deletion src/MBC7.md
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Expand Up @@ -40,6 +40,12 @@ registers. Reads return $FF. Other writes do not appear to do anything
(Partially unconfirmed). Note that you cannot re-latch the accelerometer
value without first erasing it; attempts to do so yield no change.

Once the latch for a sample update has been triggered the cpu should not be
put into HALT for at least 1.2 msec since HALTing turns off the PHI cartridge
signal (clock from the GB) which the MBC7 accelerometer sensor relies on.
If that clock is turned off too soon the X and Y values will have signficantly
more noise in the sampled data.

### Ax2x/Ax3x - Accelerometer X value (Read Only)

Ax2x contains the low byte of the X value (lower values are towards the
Expand Down Expand Up @@ -134,5 +140,5 @@ enable section as well (0000-1FFF)

## External links

- Source: [GBDev Forums thread by endrift](https://web.archive.org/web/20240429225227/http://gbdev.gg8.se/forums/viewtopic.php?id=448)
- Source: [GBDev Forums thread by endrift](https://web.archive.org/web/20250424080817/https://gbdev.gg8.se/forums/viewtopic.php?id=448)

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