Difference between revisions of "Keymap High Address Register"
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|Readable=Yes | |Readable=Yes | ||
|Writable=Yes | |Writable=Yes | ||
| − | |ShortDesc= | + | |ShortDesc=PS/2 Keymap address MSB, read (pending) first byte of palette colour |
}} | }} | ||
Write: | Write: | ||
| − | bits | + | bit 7 = 0 to select ps2 keymap, 1 to select key joystick |
| + | bits 6:1 = Reserved, must be 0 | ||
bit 0 = MSB keymap address | bit 0 = MSB keymap address | ||
Read: | Read: | ||
| − | bits 7:0 = Stored palette value from {{NextRegNo|$44}} | + | bits 7:0 = Stored first-byte palette value from {{NextRegNo|$44}} |
| − | This value does update right after writing first 8 bits of colour to NextReg $44, while the palette entry is modified only after the second write (adding ninth bit and L2 priority bit) is done. So half-written value can't be read back through {{NextRegNo|$41}}, but can be read with this register. | + | This value does update right after writing first 8 bits of colour to NextReg $44, while the real palette entry is modified only after the second write (adding ninth bit and L2 priority bit) is done. So half-written value can't be read back through {{NextRegNo|$41}}, but can be read with this register (after writing second byte to $44, this register still reads the first byte value, but the change is also committed to the palette itself and visible by reading $41 + $44 registers). |
Latest revision as of 11:35, 3 November 2024
| Number | $28 |
|---|---|
| Readable | Yes |
| Writable | Yes |
| Short Description | PS/2 Keymap address MSB, read (pending) first byte of palette colour |
Write:
bit 7 = 0 to select ps2 keymap, 1 to select key joystick bits 6:1 = Reserved, must be 0 bit 0 = MSB keymap address
Read:
bits 7:0 = Stored first-byte palette value from Enhanced ULA Palette Extension ($44)
This value does update right after writing first 8 bits of colour to NextReg $44, while the real palette entry is modified only after the second write (adding ninth bit and L2 priority bit) is done. So half-written value can't be read back through Palette Value Register ($41), but can be read with this register (after writing second byte to $44, this register still reads the first byte value, but the change is also committed to the palette itself and visible by reading $41 + $44 registers).