DISPLAY

1. Serial display consists of four 3.5 digit displays. Display is based on twelve shift registers 74HC595. Each driving one segment of the LED display. This is the cheapest way to drive segments. It is somewhat huge to solder. Serial display uses SDA, RCK, and SCL to shift segment data. The operation of the display is fully static and thus there is no need for for timing considerations. For precaution the three driving lines are buffered with 74HC04 chip. As the PCB is single sided the space requirements were huge and 595 chips with segment resistors are located on the four separate small PCBs with interconnected power and signal lines though header. One line driving PCB looks like this:
   
2. ICM7218 based miltiplexed display. Display is splitted into two four digit display with fixed decimal point. D.P. segments are used for eight status LEDs. ICM7218A chip is located on the CPU board. Displays are small of type SA39.
3. LM-11 LCD display based on HD44780-based 2x16 directly connected to port 5 of the SAB80C535 CPU. It works in 4-bit mode to conserve pins and still have busy flag readout. It uses 7 pins of the P5. See source for details on programming. LCD display has separate PCB for easy mounting on chasis and connectning through power module to CPU module. PCB also caries the four buttons for command input.
   

Main display PCB

Source

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