Delta Tau GEO BRICK LV User Manual

 

 

Turbo PMAC Servo IC SCLK Frequency Control 
On a Turbo PMAC board, or an Acc-24x with PMAC-style Servo ICs (Acc-24P or 24V), the SCLK 
frequency is set by the configuration of jumpers E34 – E38.  Only one of these jumpers may be on in any 
given configuration.  This SCLK frequency is common to all Servo ICs and channels on the board. 

Turbo PMAC2 Servo IC SCLK Frequency Control 
On a Turbo PMAC2 board, or an accessory board with PMAC2-style Servo ICs or MACRO ICs (e.g. 
Acc-24P2, 24E2, 24E2A, 24E2S, 24C2, 24C2A, 5E), the SCLK frequency is set by an I-variable for the 
Servo IC.  This variable sets the frequency for all channels in the IC, but each IC has an independent 
setting.  Consult the description of the variable in the Software Reference manual for details. 

For a PMAC2-style Servo IC m, IC variable I7m03 determines the SCLK frequency.  This variable also 
determines three other clock frequencies for the IC.  If the IC is on a MACRO Station, MI903 or MI907 
determines the SCLK frequency. 

For a MACRO IC on a Turbo PMAC2 board or UMAC Acc-5E board (for the handwheel encoders), 
I6803 determines the SCLK frequency in the same manner for both channels on the IC.  If the IC is in a 
MACRO Station with an Acc-1E stack 2-axis board, MI993 determines the SCLK frequency. 

All of these variables work in the same manner.  The other three clock frequencies that each controls are 
virtually never changed, so the following table may be useful for setting the SCLK frequency with the 
others left at the default frequency: 

2256 

39.32 MHz 

2260 

2.46 MHz 

2257 

19.66 MHz 

2261 

1.23 MHz 

2258* 9.83 

MHz*  2262 612 

kHz 

2259 4.92 

MHz 2263 

306 

kHz 

*Default 

Encoder Decode Control: I7mn0, I68n0, MI910 

The decoding of the encoder signal, both as to resolution and direction, is determined by a channel-
specific I-variable.  For Servo ICs of both PMAC-style and PMAC2-style, this is I7mn0 (for Servo IC m 
Channel n).  For MACRO IC 0 Channel n* on a Turbo PMAC (a “handwheel” port encoder), this is 
I68n0.  For encoder channels on a MACRO Station, this is node-specific variable MI910. 

This variable is set for “times-4” decode, which derives four counts per signal cycle, one for each signal 
edge.  This requires a variable value of 3 or 7.  The difference between these two values is the direction 
sense – which direction of motion causes the counter to count up.  Remember that for a feedback encoder, 
the encoder’s direction sense must match the servo-loop output’s direction sense – a positive servo output 
must cause the counter to count in the positive direction – otherwise a dangerous runaway condition will 
occur when the servo loop is closed. 

Digital quadrature encoders are processed in the conversion table with the “1/T extension” method 
(method digit $0), which uses timers associated with the counter to compute fractional count information 
that enhances smoothness of motion.  The source address specified is that of the base address of the 
channel (e.g. $78200 for Servo IC 0 Channel 1); Turbo PMAC will use several registers of that channel to 
assemble the enhanced position information automatically. 

It is also possible to disable the 1/T extension (method digit $C) in the table processing.  For details of 
setting up the encoder conversion table to process quadrature encoders, consult the Setting up the Encoder 
Conversion Table section and the specification for variables I8000 – I8191 in the Software Reference 
Manual.