G1216B1N000 dot graphics display

A serial interface and bias supply for the Seiko-Epson G1216N000 using an AT90S2313 because there just aren't enough applications examples for this display on the web. The display is a pretty old transflective gray mode TN LCD design with ok, but not great contrast. Its contrast is better than the screen shot above. The display's saving grace is that appeared to meet all of the primary criteria. The code to drive it was complicated somewhat by the fact that the 8 bit interface appears as two 64x64 displays for the left and right hand sides, and since I was determined to control it with an AT90S2313, I was a pin short of being able to have separate select pins for the left and right displays, and so implemented a Right/Left control pin, which produced some artifacts in the display, and avoiding these made it necessary to carefully code around them.
G1216B1N000 dot graphics display - schematic

The controller was implemented with an AT90S2313, but it could have been done with an AT90S1200 and a firmware UART simulation since code is pretty small and doesn't rely on the RAM or timers that an AT90S2313 provide. The hardware needs to drive the data and control lines of the Seiko-Epson module, supply an adjustable negative bias voltage and + 5 volts to the module, and provide inverting buffers for the RS-232 interface. The inverting RS-232 takes its negative supply from the host. The negative supply could have come from the LCD bias circuit (see below) but the handy thing about this circuit was that its output swung negative when connected to my RS-422 computer and only swung down to a little above ground when it was driven by the CMOS I/O port in the host on the waveform capture circuit that I connected it to after debugging. The negative bias supply was generated by making 5V peak-to-peak pulses and using them to drive a 5 stage half-wave voltage multiplier and regulating the output with an opamp. The half-wave doubler is terribly inefficient using diodes for switch such a low voltage as each doubling of the 5 volts lost nearly half of it in the diodes, but I have a lot of diodes and miniature capacitors and wanted to pass the power signal through a single 5 volt regulator to minimize the exposure of the internal circuitry to accidental hazardous voltages on the cable. A single chip switched capacitor power...

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