Next Memory Bank Select: Difference between revisions
From SpecNext Wiki
No edit summary |
mNo edit summary |
||
| (5 intermediate revisions by 3 users not shown) | |||
| Line 1: | Line 1: | ||
{{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= | |Writable=Yes | ||
|Writable= | |||
|Subsystem=Memory map | |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 {{PortNo|$7FFD}} (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 ({{NextRegNo|$03}}). In this mode the selected 16K bank comes from port 0x7ffd {bits 7:6, bits 2:0} | |||
Latest revision as of 11:45, 4 May 2020
| Port 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 NextPort:$7FFD (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 (NextReg:$03). In this mode the selected 16K bank comes from port 0x7ffd {bits 7:6, bits 2:0}