Outboard monochromator wiring

The Physical Science Laboratory SGM electronics use a Computmotor Zeta 4 driver. This has 243 $\Omega$ impedance on its Step and Direction inputs, and requires at least 6.5 mA of current to drive the optoisolators used (see pp. 17-18 of the Compumotor manual).

Our first attempt to wire up the PSL ``scan'' DB25 input to our 20 pin ribbon cables is to connect them as follows:
        J1 DIR output pin 17 $\rightarrow$ DB25 Dir+ pin 4
        J1 STEP output pin 18 $\rightarrow$ DB25 Step+ pin 3
        DB25 GND pin 24 $\rightarrow$ DB25 Dir- pin 17
        DB25 GND pin 24 $\rightarrow$ DB25 Step- pin 16
        DB25 GND pin 24 $\rightarrow$ 100 $\Omega$ $\rightarrow$ J3 pin 1         DB25 CW+ pin 5 $\rightarrow$ J3 CW pin 17
        DB25 CCW+ pin 6 $\rightarrow$ J3 CCW pin 18
This will let us test the motion of the SGM scan motor using the pre-existing EPICS configuration for the SGM_O motor by stealing the J1 and J3 ribbon cables from the old Berger-Lahr driver box.