Differences

This shows you the differences between two versions of the page.

--- sst-6809:memory_map [2025/03/16 20:49] – split main bus select 1 1k to its own page robert
+++ sst-6809:memory_map [2025/04/12 11:34] (current) – robert
@@ Line 7: / Line 7: @@
 | ::: |  E400 - E7FF  | [[Main Bus Select 1 1K]] |
 | ::: |  E800 - EAFF  | unassigned |
-| ::: |  EB00 - EBFF  | [[#ACIA Select 256b]] |
+| ::: |  EB00 - EBFF  | [[ACIA Select 256b]] |
 | ::: |  EC00 - EEFF  | unassigned |
-| ::: |  EF00 - EFFF  | [[#Memory Latch Select 256b]] |
+| ::: |  EF00 - EFFF  | [[Memory Latch Select 256b]] |
-| ROM |  F000 - FFFF  | [[#EEPROM 4K]] |
+| ROM |  F000 - FFFF  | [[EEPROM 4K]] |
 | ::: |  F000 - F3FF  | [[ASSIST09]] Expansion ROM area (unused) |
 | ::: |  F800 - FFFF  | [[ASSIST09]] |
-| MPU |  FFF0 - FFF1  | HD6390 Illegal Opcode/Divide By Zero Trap vector (FFD4) |
+| MPU |  FFF0 - FFF1  | HD6309 Illegal Opcode/Divide By Zero Trap vector (FFD4) |
 | ::: |  FFF2 - FFF3  | SWI3 vector (FFD8) |
 | ::: |  FFF4 - FFF5  | SWI2 vector (FFDC)|
@@ Line 27: / Line 27: @@
 These use J3 select jumper for 8xxx - Exxx address select range
-===== ACIA Select 256b =====
-The Status, Control, TX, and RX registers of a Motorola MC6850 or Hitachi HD6350 Asynchronous Communication Interface Adapter (ACIA) are mapped into this 256 byte page.
-The ACIA has 4 registers accessible through 2 memory mapped input/output (MMIO) addresses.
-A read from $EB00 will return the content of the ACIA Status register.
-A write to $EB00 will update the ACIA Control register with new configuration.
-A read from $EB01 will return received byte from the ACIA RX Data register.
-A write to $EB01 will update the ACIA TX Data register with a new byte to transmit.
-===== Memory Latch Select 256b =====
-The paging latch.
-Writing to it selects different blocks from the 512k to appear in the main map.
-E.g. if you write a 1 to EF00 it will duplicate the upper bank in the lower bank.
-The memory decode maps any 32k page of the 512k into $0000-$7FFF.
-The region from $8000-$DFFF is not affected by the paging register contents.
-So you can run paging code resident there.
-For that reason, it's also recommended to put any ISR's there.
-The lowest 4 paging bits control RAM, bits 4-6 select one of 8 EEPROM pages of 4k each.
-Bit 7 controls the "stat" LED
-The M command is RMW and the latch is not qualified with R/W.
-The CPU can write it but if you try doing it manually with the monitor, it will write garbage into the latch.
-If you store in a $80 it should change the status LED
-To be more specific, $80 turns the LED off and $00 turns it on as it is a pulldown and should be on at reset.
-The logic fixes ROM and I/O in place.
-When you map page 1 to page 0, only the RAM is relocated.
-So, the RAM that is hidden "under" ROM and I/O becomes visible that way.
-===== EEPROM 4K =====
-The SST-6809 contains a 32KB EEPROM.
-The Memory Latch Select allows mapping one of eight 4KB sections of the EEPROM into the memory range $F000-$FFFF which includes the MPU interrupt vectors.
-Make use of the boot ROM select jumper(s).
-The 2.0 can boot from 4 different segments, the 2.1 only 2.
-But the current EEPROM only has ASSIST09 burned into it.
-The "external ROM" is just the unused space in the other half of the 4k boot ROM.
-Ken just never put anything there.
-At some point Ken could burn another boot into an EEPROM.
-The PTM on the Mezz board can support tracing with ASSIST09, but it needs a jumper to put its interrupt on NMI.
 Return to [[:SST-6809:]]

Exile In Paradise

Stranded on Earth...

Differences