Model 7002Switch System Instruction Manual - Advanced Test ...

Theory of Operationthe TXD line to the PD0 terminal of the microcontroller. Ina similar manner, light pen data is serially sent back to thedigital board through the RXD line via PD1.There are two latching circuits configured around the flipflopsof U510. One latching circuit controls the /CTS (Clearto Send) line. When the light pen is clicked, the output of theflip-flop goes high for 5msec. During this period, new serialindata is held off to allow current data to be processed. Theother flip-flop latches the output signal of the light pen whenthe light signal from the LED is detected.LEDMatrixThe serial-in and serial-out data for the microcontroller issimilar to RS-232 communications except that TTL levelsare used. The communication parameters for both send andreceive are as follows:9600 baudNO parity8 data bits1 start bit1 stop bitColumnDriversRow Drivers+6VRESETMicro-ControllerLightPenThe +6V supply (Vcc) is used to drive the LEDs, while the+5V supply is used to power all the other circuits on theboard. Crystal (Y501) is used to generate the 4MHz displayclock.Figure 6-8LED display board block diagram6.7 External control signalsAs shown in the schematic (drawing 7002-156), the LEDsare arranged in five matrices (two slots per matrix). A matrixformat minimizes the number of microcontroller peripherallines required to read and control LEDs. An LED that isclocked by the light pen is read by strobing the columns andreading all rows to detect the light strobe. The data for thatLED is then interpreted by the LED display microcontrollerand sent back to the main microprocessor on the digitalboard using proprietary encoding schemes. Coded data isthen sent to both display boards to update the VFD messagesand the state of the LEDs.The microcontroller selects columns by turning on the appropriateN-channel MOSFET (Q501 through Q511). Thecontrol LEDs for the light pen make up the eleventh columnand are controlled by Q507. The microcontroller selectsrows by controlling the source drivers (U505 through U509).CHANNEL READY and EXTERNAL TRIGGER are TTLcompatible,and support communication with existing instrumentproducts or other user-supplied equipment throughBNC connectors.TRIGGER LINK (see Figure 6-9) consists of six TTL-compatiblesignals that can be bused between instruments via apair of 8-pin TRIGGER LINK IN and TRIGGER LINKOUT micro-DIN connectors located on the Model 7002 rearpanel. The TRIGGER LINK can be programmed in asynchronousmode to operate as an additional CHANNELREADY or EXTERNAL TRIGGER signal, or in semi-synchronousmode.DIGITAL I/O (see Figure 6-10) has four programmable outputs,one TTL output, and an additional line that provides externalpull-up voltage for the outputs. DIGITAL I/O isprovided through a DB-9 connector located on the Model7002 rear panel.All external control signals can be controlled through thefront panel or programmed via the IEEE-488 bus.6-10