The Keyboard And Keyboard Display; Printer; Printer Gate Array; Printer Ram - HP PageWriter XL M1705B Service Manual

The Keyboard and
Keyboard Display
The keyboard and the keyboard display constitute the front panel
controls and indicators. They share a connector that plugs into the
CPU assembly at Jl (refer back to Figure 5-2). Pin assignments for
Jl are listed in Appendix A.
The keyboard consists of the control switches, the alphanumeric
keyboard, and the LED indicators. The keyboard communicates
with the CPU assembly over serial transmit and receive lines. The
system reads keycode information on the transmit line, and writes
LED indicator information on the receive line. While the cardiograph
is in Standby, the [On-Standby) key is connected to the system by a
separate signal line; when the cardiograph is On, the [On-Standby) key
is also encoded like the other keys. The AC indicator is driven by the
system through a separate signal line.
The keyboard display is a 40-character, 2-line, alphanumeric LCD.
It receives 8-bit data from the system, and control signals from the
FGA.
Printer
The cardiograph's printer consists of the control and drive circuitry
on the main circuit board, the thermal printhead, and the paper
transport mechanism. The block diagram in Figure 5- 11 shows how
these parts connect to each other and to the rest of the cardiograph.
Printer Gate Array
The printer gate array is the principal component of the printer
control circuitry. It buffers print data coming from the system and
status data going to the system, controls printer timing, controls the
printer RAM, regulates motor speed, monitors printhead temperature
and resistance, monitors the battery condition, and provides the
interface between the printer and the system CPU.
Printer RAM
The printer RAM consists of 32 kilobytes 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.
5-22 Theory of Operation