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Talking to Turbo PMAC 

43 

The following table shows how the jumpers (Turbo PMAC boards) or DIP switches (Turbo PMAC2) set 
the base address on the ISA or PC/104 port.  A PMAC jumper that is OFF or a PMAC2 DIP-switch that is 
OPEN adds the associated bit value to the base address; a jumper that is ON or a DIP-switch that is 
CLOSED adds nothing to the base address value. 

15 14 13 12 11 10 9 8 7 6 5 4 

x x x x 

E91 

E92 

E66 

E67 

E68 

E69 

E70 

E71 

12 11 10  9  8 7 6 5 4 3 2 1 

32768 16384  8192  4096  2048 1024  512  256  128  64  32  16 

$8000 $4000 $2000 $1000 $800 $400 $200 $100  $80  $40  $20  $10 

- - - - 

ON 

ON 

OFF 

ON 

ON 

ON 

ON 

OFF 

CLS CLS CLS CLS CLS CLS OPN CLS CLS CLS CLS OPN 

PCI Bus 
The PCI bus interface comes standard on board-level Turbo PMAC controllers with the –PCI suffix (e.g. 
Turbo PMAC-PCI, Turbo PMAC2-PCI).  The UMAC-CPCI Turbo CPU board has been designed to 
accept a daughter board that implements the Compact PCI interface, a rack-mounted version of the PCI 
bus (equivalent electrically and in software), but as of this writing the CPCI daughter board has not been 
implemented. 

The basic communications on the PCI bus goes through the host port on the Turbo PMAC’s CPU. Dual-
ported RAM is an optional addition to this bus interface (see below).  The address of the host port 
communications in the I/O space of the PCI bus is selected by the host computer’s operating system.  
Recent Microsoft Windows operating systems do this on a plug-and-play basis.  The design of the PCI 
bus interface on Turbo PMACs was implemented to be as much as possible like the older ISA bus 
interface, to minimize any transition problems from users changing over from ISA.  Other than the 
automatic address setting, the software interface to the PCI bus on Turbo PMACs is identical to that for 
the ISA bus. 

VME Bus 
The VME bus interface comes standard on board-level Turbo PMAC controllers with the –VME suffix 
(e.g. Turbo PMAC-VME, Turbo PMAC2-VME).  It is a slave interface on the bus, and can be used with 
16, 24, and 32-bit addressing on the bus.  The address, bus width, and other details of the interface are set 
by the values of Turbo PMAC variables I90 – I99 at power-up/reset.  The factory default setting is for 24-
bit addressing, with a base address of $7FA000 on the VME bus. 

The most basic communications on the VME bus goes through a set of 16 mailbox registers in the VME 
interface IC on the Turbo PMAC, each capable of holding one character.  Note that unlike the other 
buses, this communications does not go through the Turbo CPU’s host port, so it is not possible to 
download new operational firmware in bootstrap mode to the Turbo PMAC over the VME bus.  Dual-
ported RAM is an optional addition to this bus interface (see below), but one that is virtually always used.  
If DPRAM is present, usually it is easier to send text commands through the DPRAM, and the mailbox 
registers are typically not used. 

The following table shows how I90 – I99 should be set for 24-bit and 32-bit addressing (16-bit is almost 
never used), with and without dual-ported RAM.  The values in the table are for a mailbox base address 
on the bus of $abcdef00, and a DPRAM base address of $abg00000 (a and b are not used in 24-bit 
addressing). 

24-bit, 

no 

DPRAM 

$29 $04 * $cd $ef ** **  * $60 $10 

24-bit, w/ DPRAM 

$29 

$04 

* 

$cd 

$ef 

** 

** 

$0g 

$E0 

$90 

32-bit, 

no 

DPRAM 

$39 $04 $ab $cd $ef ** **  * $60 $10 

32-bit, w/ DPRAM 

$39 

$04 

$ab 

$cd 

$ef 

** 

** 

$0g 

$E0 

$90