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Peek 2070L Operating Manual - Quality Traffic Systems

Peek 2070L Operating Manual - Quality Traffic Systems

Section 6 — Theory of

Section 6 — Theory of Operation6.2.4 Field I/O ModuleThe primary purpose of the Field I/O module isto provide electrical connections between theother modules of the 2070 (primarily the CPUmodule) and the traffic cabinet in which thecontroller is housed. The module functionsboth as a pass-through for serial port 3 andmulti-drop for serial port 5 on to the C12Sconnector, and as a translator of externalcabinet data onto serial port 5, where theinformation can be passed to the 2070 CPU.Connectors C1S and C11S provide thecontroller with access to the field inputs andoutputs available in the cabinet (things likepedestrian switches, vehicle sensors, signalstates, etc.) These two connectors are locatedon their own circuit board which is attached tothe main Field I/O PCB across an Interconnectheader. The header is simply a one-to-onerouting of pins to the Input Conditioner andOutput Buffer. The Input Conditioner functionsas a voltage divider to bring the 24V logicalsignals from the field down to 5V logicalsignals suitable for the digital circuitry on theField I/O board. Pin O39 on the Output bufferserves as the controller’s heartbeat signal foran external monitor.The input and output buffers, the DSP, the68302 microcontroller, the memory locations,and the associated components are all usedto handle the connection between the CPU’sSP5 serial port and the cabinet signals.There are two data/address busses (linked bythe Dual Port RAM.) The left side busconnects the 68302 microcontroller to themodule’s EPROM and SRAM memory. Duringthis operation, the microcontroller uses its buscontrol to send data to and from memory. Themicrocontroller runs its firmware from theEPROM and stores its data and variables inthe SRAM module. Unlike on the CPUmodule, the Field I/O SRAM is allowed to loseits contents upon power down. During left busoperation, the microcontroller also sends datato and from the CPU along the SP5 serialchannel.Figure 21 – Field I/O Module block diagram42 • Model 2070L Operating Manual

Detailed Systems DescriptionThe right side bus connects the DSP to the input and output buffers andassociated circuits. The DSP uses its bus control to bring data in from theinput buffers and send data out to the output buffers, with the assistance ofthe I/O Control. The output buffers act as current drains.However, these two busses can also connect to one another. The Dual PortRAM is accessed at different times by the DSP and the MC68302Microcontroller. The two data busses stay separate until one or the other ofthese devices ‘opens the channel’ between them. This could be themicrocontroller sending a message to the DSP that it needs the values on aset of inputs, or that a set of outputs need to be changed. The DSP canopen the channel when it has the data to pass back to the microcontroller.The C12S connector provides access to SP3 and SP5, and providesNRESET, LINESYNC, and POWERDOWN signals to external devices.However SP3 may be deactivated. If a comms or serial card is installed inslot A1 of the 2070 chassis, its top port will default to use SP3 forcommunications. This can cause serious comms problems. If a comms cardis installed in slot A1, the SP3 output to the C12S connector on the Field I/Omodule must be deactivated. This is done using the S1 switch, whichdisconnects the SP3 channel at two points: outside of the power isolationarea near the backplane connector, and at the power isolated TTLEIA485converter near the C12S connector. If the S1 switch is set ON, meaning thatthe SP3 port on the Field I/O module is enabled, the SP3_ACTIVE LED onthe module will be illuminated as well.We mentioned earlier that pin O39 on the Output Buffer functions as the2070 ‘heart beat’ provided to the outside world. Devices outside of thecontroller simply watch this channel to verify that it changes state at leastonce every 1 or 1.5 seconds. This pin is driven with the assistance of theWatchdog circuit, which is included on the Field I/O module to handle theheart beat signal during power up. This O39 heart beat is normally providedas part of the CPU’s regular operation directives to the Field I/O module tochange the states of its outputs. When the 2070 is first powered on,however, the CPU does not usually provide this signal for a couple ofseconds, until it gets up and running. Now, most conflict monitors do nothave an issue with the lack of a heartbeat signal during the first 10 secondsafter the 2070 is turned on. But a model 210 Conflict monitor will detect thelack of a heartbeat during this time and kick the intersection into flash.To prevent this, the Watchdog circuit, working in conjunction with theMC68302 microcontroller, provides the heart beat signal to pin O39 until theCPU has gotten up, brushed its teeth, and had a cup of coffee, at whichpoint the CPU can take over the generation of the heart beat signal and theWatchdog goes back into a passive mode. Any time the power is interruptedlong enough to cause a POWERUP and CPU_RESET signal to come inalong the backplane, the Watchdog circuit will perform this duty. (Good dog!)Model 2070L Operating Manual • 43

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