Difference between revisions of "Next Memory Bank Select"
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{{Port | {{Port | ||
|Number=$DFFD | |Number=$DFFD | ||
+ | |NumberDec=57341 | ||
+ | |PortMask=%1101 1111 1111 1101 | ||
|ShortDesc=Provides additional bank select bits for extended memory. | |ShortDesc=Provides additional bank select bits for extended memory. | ||
|Readable=No | |Readable=No | ||
|Writable=Yes | |Writable=Yes | ||
|Subsystem=Memory map | |Subsystem=Memory map | ||
− | |||
}} | }} | ||
: bit 7 = 1 to set pentagon 512K mode (hard reset = 0) † | : bit 7 = 1 to set pentagon 512K mode (hard reset = 0) † |
Latest revision as of 11:45, 4 May 2020
Number | $DFFD |
---|---|
Decimal | 57341 |
Short desc. | Provides additional bank select bits for extended memory. |
Bit Mask | %1101 1111 1111 1101 |
Readable | No |
Writable | Yes |
Subsystem | Memory map |
- bit 7 = 1 to set pentagon 512K mode (hard reset = 0) †
- bits 3:0 = most significant bits of the 16K RAM bank selected in Memory Paging Control ($7FFD / 32765) (soft reset = 0)
Port 0xDFFD bits 3:0 are combined as the highest bits with the bank selected in port 0x7FFD to form a 7-bit bank number.
Bit 7 can only be modified when pentagon timing is not active.
† Pentagon 512K mode is applied only when the machine is set to pentagon timing (Machine Type Register ($03)). In this mode the selected 16K bank comes from port 0x7ffd {bits 7:6, bits 2:0}