Muon Calibration System Arcnet Software - PLM  3/2/2000

The arcnet interface in the muon calibration system is used to download a 
pulse height value into a DAC as well as turning on the appropriate driver 
channels. There is one DAC card common to all driver boards. Each driver
board has 8 output channels which are enabled via mask bits. These drivers 
then pulse anode wires in the muon tracking chambers when commanded by 
the Glink interface.

The downloading procedure starts by setting up the 11 control and data lines
(defined below) with 9 bits of data set low, a clock low, and a clear high.
Then a clear (low, then high) is issued. Next the DAC serial data line is set
to the msb (D7) of the DAC value and each of the eight driver card lines are
also set to their mask msbs. The mask bits are defined as 1=ON, 0=OFF. Then
the clock is driven (high, then low), which latches the first data bit. The
process is  continued by setting  the 9 lines to the (D6) bit, clocking and so
on until the lsb (D0) has been latched.

We use the chip select bits of the generic arcnet board (CS2 through 15) for
the control and data lines.  They are assigned as follows :

Clock line		CS2		clocks on rising edge
Clear line		CS4		clears low
DAC serial data line	CS6		true data, msb first, lsb last
Driver #1 serial data	CS8			"
            #2		CS9			"
            #3		CS10			"
            #4		CS11			"
            #5		CS12			"
            #6		CS13			"
            #7		CS14			"
            #8		CS15			"

CS0, 1, 3, 5, and 7 are not used.

So the sequence looks something like the following, going from left to right
for a total of 8 patterns latched in plus one clear at the beginning:

           ArcNet        1st      last
Line       output clear data      data
-----      ------ ----- ----      ----
Clock       CS2     0    010  ...  010
Clear       CS4    101    1   ...   1
DAC         CS6     0     D7        D0
Driver #1   CS8     0     D7        D0
Driver #2   CS9     0     D7        D0
Driver #3   CS10    0     D7        D0
Driver #4   CS11    0     D7        D0
Driver #5   CS12    0     D7        D0
Driver #6   CS13    0     D7        D0
Driver #7   CS14    0     D7        D0
Driver #8   CS15    0     D7  ...   D0

* where at 1 means high and 0 low; and 101 means pulse line high, then low,
  then high; and similarily for 010.

Demonstration software, written in LABVIEW, can download the DAC and one driver
card through a PC parallel port interface on the front of the DAC module. This
code is working and provides a nice example of how the load the calibration
system. We have not determined how fast the downloading can proceed, but the
chips are capable of being clocked at about 1 MHz.