Toshiba HX 34 mapper
zeilemaker54 edited this page Jun 5, 2021
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3 revisions
7FFF = x01xxxxx
- SRAM accessable at 08000H-0805FH and 08080H-087FFH
- Readback vdp registers at 08000H-0805FH disabled
- Readback registers are NOT updated
- Address latch readback (and other unknown locations) at 08060H-0807FH (readonly)
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- 08060H = 11111xxx (xxx = value of VDP register 14 at the last VRAM read or write)
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- 08061H = 0yxxxxxx (xxxxxx = high byte VRAM address at last VRAM read or write, y = 0 when read, y = 1 when write)
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- 08062H = xxxxxxxx (xxxxxxxx = low byte VRAM address at last VRAM read or write)
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- address latch readback (08060H-8062H) updated
7FFF = x11xxxxx
- SRAM accessable at 08080H-087FFH
- Readback vdp registers at 08000H-0805FH enabled, but writeable!
- Readback registers are NOT updated
- Address latch readback (and other unknown locations) at 08060H-0807FH (readonly)
-
- 08060H = 11111xxx (xxx = value of VDP register 14 at the last VRAM read or write)
-
- 08061H = 0yxxxxxx (xxxxxx = high byte VRAM address at last VRAM read or write, y = 0 when read, y = 1 when write)
-
- 08062H = xxxxxxxx (xxxxxxxx = low byte VRAM address at last VRAM read or write)
-
- address latch readback (08060H-8062H) NOT updated
indirect VDP register access is supported by the readback registers. 7FFF = x01xxxxx (and x10xxxxx) is not used by the firmware. So if the goal is to support the HX3x firmware in OpenMSX, the emulation of these modes could be dropped.