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

Theory of OperationID CLK1 8 9IDDATA(Data outputfrom mainframeor ROM)IDDATA(Data outputfrom mainframeor ROM)StartAcknowledgeFigure 6-5Timing diagram, IDCLK and IDDATAID CLKID DATAStart BitFigure 6-6Start and stop sequences6.4.4 Relay controlStop Bit6.4.5 Power-on safeguardA power-on safeguard ensures that relays do not randomlyenergize on power-up and power-down. This safeguard disablesthe relay drivers on the switch cards during power-upand power down.When the 68302 microprocessor goes in the RESET mode,line PB7 (OUTPUT ENABLE) on U110 goes high disablingall relay drivers. After the RESET condition clears, PB7 goeslow and enables all the relay drivers. Note that PB7 stays low(enabling the relay drivers) until the 68302 microprocessorgoes into a reset condition.Card relays are controlled by serial data transmitted via therelay DATA line. Five bytes for each card are shifted in serialfashion into latches located in the card and backplane relaydriver ICs. The serial data is clocked in by the CLK line. Asdata overflows one register, it is fed out the Q’s line of theregister down the chain.6.5 VFD display board circuitryA block diagram of the VFD display board is shown in Figure6-7. Major components include the display microcontroller,the dot and grid drivers, the vacuum fluorescent display(VFD), and the key matrix.Once all five bytes have been shifted into the drivers, theSTROBE line is set high to latch the relay information intothe Q outputs of the relay drivers. The appropriate relays arealso energized (assuming the driver outputs are enabled, asdiscussed below). Note that a relay driver output goes low toenergize the corresponding relay.The 68HC05 (U402) is the display microcontroller that controlsthe VFD and interprets key data. The microcontrollerhas four peripheral I/O ports, which are used for the variouscontrol and read functions. Display data is serially transmittedto the microcontroller from the digital board via the TXBline to the microcontroller PD0 terminal. In a similar manner,key data is serially sent back to the digital board throughthe RXB line via PD1.6-8