CHAPTER 3
3.4.3 Status Circuitry
Figure 3-5 shows the Status circuitry. This circuitry allows the Micro Controller to monitor all the operational status of the basic printer. On the left are Card, Ribbon panel, Flag, Head Latch, and Head up/Down Sensors. Below these appear the Print Head Temperature Sensing Thermistor.
Programmable resistors inside U20 set the threshold levels of U17 analog comparators a through d and the LED intensity of the Card and Ribbon Sensors. The Micro Controller can check the states of the analog comparators and the status of the Head Latch Sensor by loading and then reading registers U31 and U32.
The Flag sensor produces pulses at the R FILM T signal at a rate proportional to ribbon supply spindle rotation. Without corrective action, the rate would increase as ribbon collects on the Take Up Spindle and increases its diameter. However, by keeping track of the number of pulses generated for each complete ribbon panel sequence, the Micro Controller has a basis for Ribbon Take Up Motor control. The Micro Controller reduces motor rotation sufficiently to keep the number of pulses approximately equal for each imaging sequence. The result serves to keep color imaging passes within the confines of respective ribbon panels.
The Print Head raises for fast card transports and lowers for imaging. LED-Photo transistor sensors signal related Head Up and Head Down status. Cutouts on a disk align with the sensors to signal these events. The disk attaches to the shaft of the Head Up/Down Motor.
As noted in the Motor Control descriptions, U20, and associated programable resistors, receive control from the Micro Controller via the Serial Data line (SD1) in step with the Serial Data Clock (SDK). The CS POT signal chip-enables U20.
