Reference Manual

Turbo PMAC/PMAC2 Software Reference

Turbo PMAC Global I-Variables 48

I20 MACRO IC 0 Base Address (Turbo PMAC2 only)

Range: $0, $078400 - $07B700

Units: Turbo PMAC2 Addresses

Default: Auto-detected

I20 sets the base address of the first MACRO IC (called MACRO IC 0) in the Turbo PMAC2 system,

normally the one with the lowest base address. A setting of 0 for I20 tells the Turbo PMAC2 CPU that no

MACRO IC 0 is present, and none of the firmware’s automatic functions for that IC will be active.

On re-initialization – either on resetting with the E3 re-initialization jumper ON or on issuing the

$$$*** command, Turbo PMAC2 will auto-detect which MACRO ICs are present, and set I20 to the

base address of the MACRO IC with the lowest base address. Turbo PMAC2 will also do this when

commanded to set I20 to its default value (I20=*). If no MACRO ICs are found, I20 will be set to 0

instead.

If automatic use of the multiplexer port or the display port is desired, I20 must be set to the base address

of the DSPGATE2 IC serving as MACRO IC that is connected to this port. In UMAC Turbo systems it is

possible to have multiple multiplexer and display ports, but only those ports connected to the single IC

selected by I20 support the automatic firmware functions for those ports. In other Turbo PMAC2

systems, the on-board multiplexer and display ports using the MACRO IC at $078400 are always used,

regardless of the setting of I20.

I-variables I6800 – I6849 reference registers in MACRO IC 0, whose addresses are relative to the address

contained in I20. These addresses are established at power-up/reset. If the value of I20 is incorrect at

power-up/reset, these I-variables will not work. It is possible to set the value of I20 directly, saving the

value and resetting the card, but users are strongly encouraged just to let Turbo PMAC2 set I20 itself by

re-initialization or default setting, and to treat I20 as a status variable. If I20 is set to 0, these variables

will always return a value of 0.

A Turbo PMAC2 will look to find MACRO nodes 0 – 15 in MACRO IC 0, referenced to the address

contained in I20. These addresses are established at power-up/reset. If the value of I20 is incorrect at

power-up/reset, these MACRO nodes will not be accessed.

UMAC versions of the Turbo PMAC2 have the addressing capability for up to 16 MACRO ICs, but only

the 4 MACRO ICs referenced by I20 – I23 can have I-variable support. Master-to-master MACRO

communications can only be done on MACRO IC 0, referenced by I20, when I84=0.

For a Turbo PMAC2 that is not Ultralite or UMAC, the only valid MACRO IC 0 base address is

$078400. For a Turbo PMAC2 Ultralite, the valid base addresses are $078400, $079400, $07A400, and

$07B400. For a UMAC Turbo system, the valid base addresses can be expressed as $07xy00, where x

can be 8, 9, A, or B, and ‘y’ can be ‘4’, ‘5’, ‘6’, or ‘7’.

If the configuration of the MACRO ICs in a modular Turbo PMAC system, such as a UMAC Turbo rack,

is changed, the values of I20 – I23 will need to be changed.