Difference between revisions of "Expansion Bus Enable Register"

Revision as of 23:58, 4 December 2019

Number	$80
Readable	Yes
Writable	Yes
Short Description	Expansion bus enable/config

Bit	Description
	Values affecting machine immediately
7	1 to enable Expansion Bus
5	1 to disable I/O cycles and ignore IORQULA
4	1 to disable memory cycles and ignore ROMCS
	After soft reset (will be copied to bits 7-4)
3	1 to enable Expansion Bus
1	1 to disable I/O cycles and ignore IORQULA
0	1 to disable memory cycles and ignore ROMCS

Set to 0 upon hard reset.

(new register since core 3.0.5)

(note: Next registers with number higher than $7F are inaccessible from Copper code)

@@ Line 3: / Line 3: @@
 |Readable=Yes
 |Writable=Yes
-|ShortDesc=Expansion bus controls/config
+|ShortDesc=Expansion bus enable/config
 }}
-Read (may change in the future):
 {|class="wikitable"
 ! Bit !! Description
 |-
-| 7 || ROMCS is being asserted on the expansion bus
+|  || Values affecting machine immediately
 |-
-| 6 || Expansion bus is currently enabled
+| 7 || 1 to enable Expansion Bus
 |-
-| 5 || Max clock is always propagated to the expansion bus
+| 5 || 1 to disable I/O cycles and ignore IORQULA
 |-
-| 4 || 0 indicates the 48K rom is locked in place
+| 4 || 1 to disable memory cycles and ignore ROMCS
 |-
-| 3-2 || Reserved
+|  || After soft reset (will be copied to bits 7-4)
 |-
-| 1-0 || Max cpu speed while the expansion bus is enabled
+| 3 || 1 to enable Expansion Bus
-|}
-Write (may change in the future):
-{|class="wikitable"
-! Bit !! Description
-|-
-| 7 || Make change immediate otherwise changes are noted for next soft reset
-|-
-| 6 || Enable the expansion bus (hard reset = 0)
 |-
-| 5 || Always propagate the max clock to the expansion bus (hard reset = 0)
+| 1 || 1 to disable I/O cycles and ignore IORQULA
 |-
-| 4 || 0 to lock the 48k rom in place (hard reset = 0)
+| 0 || 1 to disable memory cycles and ignore ROMCS
-|-
-| 3-2 || Reserved, must be 0
-|-
-| 1-0 || CPU speed when the expansion bus is enabled (currently fixed at 00 = 3.5 MHz) (hard reset = 00)
 |}
+Set to 0 upon hard reset.
+(new register since core 3.0.5)
 (note: Next registers with number higher than $7F are inaccessible from Copper code)