Reference Manual

Turbo PMAC/PMAC2 Software Reference
Turbo PMAC Global I-Variables 202
In any Turbo PMAC2 system, there must be only one source of servo and phase clock signals for the
system – either one of the Servo ICs or MACRO ICs, or a source external to the system. Only in a 3U-
format Turbo PMAC2 system (UMAC Turbo or 3U Turbo Stack) can the system clock signals come from
an accessory board. In all other Turbo PMAC2 systems, the system clock signals must come from and IC
on the base PMAC2 boards, or be brought from an external source through the serial port.
These variables are 2-bit values on DSPGATE2 MACRO ICs, but only 1-bit values on MACROGATE
MACRO ICs. Bit 0 is set to 0 for the IC to use its own Phase clock signal and output it; it is set to 1 to use
an externally input Phase clock signal. Bit 1 (DSPGATE2 only) is set to 1 for the IC to use its own Servo
clock signal and output it; it is set to 1 to use an externally input Servo clock signal. This yields four
possible values for I6807 (etc.):
 I6807 = 0: Internal Phase clock; internal Servo clock
 I6807 = 1: External Phase clock; internal Servo clock
 I6807 = 2: Internal Phase clock; external Servo clock
 I6807 = 3: External Phase clock; external Servo clock
In all normal use, I6807 (etc.) is either set to 0 (on at most one IC) or 3 (on all the other ICs – 1 on
MACROGATE ICs).
In typical use of the Turbo PMAC2 Ultralite, MACRO IC 0, whose Phase clock frequency is controlled
by I6800 and I6801, will generate the Phase clock signal for the entire board, so I6807 is set to 0, and
I6857, I6907, and I6957 should all be set to 1.
Note:
A MACROGATE MACRO IC cannot generate a servo clock signal internally.
Therefore, it cannot be used to provide the system clocks for the Turbo PMAC2
system.
During re-initialization, Turbo PMAC2 determines which IC it will use as the source of its system Phase
and Servo clock signals, setting I19 to the number of the clock-direction I-variable whose IC is selected as
the source. This clock-direction I-variable is then automatically set to 0; all other clock-direction I-
variables are set to 1 or 3. Most users will never change these settings.
When a clock-direction I-variable is commanded to its default value (e.g. I6857=*), Turbo PMAC2
looks to the value of I19 to determine whether this I-variable is set to 0 or 3 (0 or 1 on a MACROGATE
IC).
On the reset of a 3U-format Turbo PMAC2 system (UMAC Turbo or 3U Turbo Stack), the values set for
these I-variables are determined by the saved value of I19, and not by the saved values of these I-
variables themselves. On these systems, to change which IC is the source of the system clocks, change
the value of I19, save this setting, and reset the card.
To change which IC is the source of the system clocks in other Turbo PMAC2 systems, it is best to
change both clock-direction I-variables on a single command line (e.g. I6807=1 I7007=0), then
SAVE these new settings.
If all of the Servo ICs and MACRO ICs in a Turbo PMAC2 system have been set up for external phase
and servo clocks, but these clock signals are not provided, the Turbo PMAC2 will trip its watchdog timer
immediately.
Channel-Specific MACRO IC I-variables
(For MACRO IC Channel n*, where n* = 1 to 2)
I-Variables in the I6810s, I6820s, I6910s, and I6920s control the hardware aspects of the MACRO IC
DSPGATE2 ASIC that provides the machine interface for supplemental channels 1 and 2. Note that few
of these functions are used on the Turbo PMAC2s. By default, only the two encoder inputs and the two
C-channel PWM/PFM outputs are used. These I-variables are not active if the MACRO IC is not present,
or is a MACROGATE IC.