Commodore 128 Programmer's Reference Manual page 473

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THE COMMODORE 128 OPERATING SYSTEM 463
corresponds to LCR B, and so on). The format for the Load Configuration and
Preconfiguration Registers is the same as for the Configuration Register. The four LCRs
and four PCRs are all initialized to zero.
I \
$FFQ4
$FF03
$FFQ2
$FF01
$FF0O
LCRD
LCRC
LCRB
LCRfl
CR
$D50B
$D50R
$D509
$D508-
$D507-
$D506-
$D505-
$D503.
$D502
$D501
$D500.
VR
PIH
PIL
PGH
POL
RCR
MCR
PCRD
PCRC
PCRB
PCRfl
CR
LORD CONFIGURRTION REG fl
CONFIGURflTION REGISTER
JpRECONFIGURRTION REGISTER fl
CONFIGURflTION REGISTER
Figure 13-6. MMU Register Map
To directly change the value of the Configuration Register (therefore bypassing
the preconfiguration mechanism), perform a write operation (STA, STX, STY) directly
to the Configuration Register at either $D500 or $FF00.
To indirectly change the value of the Configuration Register (therefore utilizing
the preconfiguration mechanism), perform a write operation (STA, STX, STY) to the
Preconfiguration Register. This loads a value into the PCR. When a subsequent store
instruction is performed to the corresponding Load Configuration Register, the value
that was previously stored in the corresponding PCR is loaded into the CR. The store
instruction acts as a triggering mechanism that passes the contents of a PCR into the CR.
When a store instruction is executed upon an LCR, the value in the corresponding PCR
is loaded into the CR and memory management organization conforms to the value
associated with that PCR.
For example, to alter the memory management organization specified on power-up,
use the following machine language segment: