Service manual

CPU Assembly
3-8
timing and the printer RAM, regulates motor speed, monitors printhead temperature,
monitors the battery condition, and provides the interface between the printer and the
system CPU.
The printer RAM consists of 32K of static RAM used to store printer data and the printer
look-up table data. The look-up table data is used to compensate the motor drive signals
and the printer enable pulses for variations in the operating environment. The look-up
table data also includes the motor settings and the motor ramp-up profile.
Motor Driver
The phase signals from the printer gate array enable the motor driver circuit, which
switches current through the stepper motor in the paper transport.
Analog/Digital Converter
This 8-bit parallel A/D converter measures printhead temperature, battery voltage, and
printer supply voltage.
Thermal Printhead
The thermal printhead is a line of 1728 printing elements. Each printing element is a
resistive heater. Heat from these elements blackens the thermoreactive paper, creating an
image. A 1728-bit shift register (on the printhead) contains the dot data for the print line.
Data is serially loaded into the shift register, then latched so that data for the next line may
be shifted into the head while the present line prints. A strobe signal enables printing. The
pulse width of the strobe is adjusted to compensate for different recording speeds and
variations in supply voltage, average resistance, and temperature. The temperature is
sensed by a thermistor on the printhead heat sink.
System Expansion Connector
The System Expansion Connector provides the instrument with future expansion
capability, such as Option #A05, #A10.