Reference Manual

PMAC 2 Software Reference
390 PMAC Saved Setup Registers
X:$0786 VME Mailbox Base Address Bits A23-A16
ISA DPRAM Base Address Bits A23-A16
Range: $00 - $FF
Units: None
Default: $7F (VME); $0D (ISA)
On VME bus systems, X:$0786 controls bits A23 through A16 of the VME bus base address of the
mailbox registers for PMAC. Bit 7 of X:$0786 corresponds to A23 of the base address, and bit 0 of
X:$0786 corresponds to A16. X:$0786 is only used on VME systems if 24-bit or 32-bit addressing has
been selected with X:$0783 and X:$078C.
On ISA bus systems (PC, PC Ultralite), X:$0786 controls bits A23 through A16 of the ISA bus base
address of the DPRAM. Bit 7 of X:$0786 corresponds to A23 of the base address, and bit 0 of X:$0786
corresponds to A16. A23 through A20 are only used on ISA bus systems if bit 2 of X:$0787 is set to 1,
enabling 24-bit addressing.
X:$0786 is actually used at power-on/reset only, so to set or change the base address, change the value of
X:$0786, store this new value to non-volatile flash memory with the SAVE command, and reset the card
with the $$$ command. The active register into which the value of X:$0786 is copied at power-on/reset
is X:$E009 bits 0 – 7. It is permissible to write to this register directly (suggested M-variable M93) to
change the active setup without a SAVE and reset.
X:$0787 VME Mailbox Base Address Bits A15-A08
ISA DPRAM Base Address Bits A15-A14 & Control
Range: $00 - $FF
Units: None
Default: $A0 (VME); $45 (ISA)
On VME bus systems, X:$0787 controls bits A15 through A08 of the VME bus base address of the
mailbox registers of PMAC. Bit 7 of X:$0786 corresponds to A23 of the base address, and bit 0 of
X:$0786 corresponds to A16. X:$0787 is used whether 16-bit, 24-bit, or 32-bit addressing has been
selected with X:$0783 and X:$078C.
On ISA bus systems (PC and PC Ultralite), X:$0787 controls the enable state and addressing mode of the
DPRAM. If the DPRAM is to appear as a 16k block of memory on the ISA bus, it also sets bits A15 and
A14 of the ISA bus base address.
The first hex digit of X:$0787 contains bits 4 – 7. When the DPRAM is addressed as a 16k x 8 block of
memory on the ISA bus, bit 7 of X:$0787 corresponds to A15, and bit 6 of X:$0787 corresponds to A14.
Bits 5 and 4 must be set to 0.
The second hex digit of X:$0787 contains bits 0 – 3. These are individual control bits. Bits 0 and 2
control the addressing mode and block size. Bits 1 and 3 control the bank selection if the large DPRAM
is addressed as a small block of memory. These should always be set to 0 in a non-Turbo PMAC. The
commonly used settings of the second hex digit of X:$0787 are:
• 0: DPRAM not enabled
• 1: 20-bit addressing (below 1M), 16k x 8 address block
• 5: 24-bit addressing (above or below 1M), 16k x 8 address block
X:$0787 is actually used at power-on/reset only, so to set or change, and keep, these settings, change the
value of X:$0787, store this new value to non-volatile flash memory with the SAVE command, and reset
the card with the $$$ command. The active register into which the value of X:$0787 is copied at power-