Keypad Interface; Printhead Control - GE MAC 1200 Servicing Instructions

GE Medical Systems MAC 1200 V 1.2 Page 17
Information Technologies 227 492 21 Rev F
LCD Power Supply:
The LCD power supply VEE of -23V is generated from the +5V logic supply. The
generation starts after HRESET_ becomes inactive to ensure that the logic supply of +5V
first is applied to the display.
Adjusting Contrast:
Contrast adjustment of the Display is accomplished with the contrast voltage VO. The level
of VO is controlled with the PWM signal BLCD_CONTR from the timer module of the
MPC821. In addition, the contrast voltage is temperature compensated.
Backlight:
The LCD backlight converter for the CCFL tube is located on the PCB Control CS CI too.
The backlight converter is generated from the +5V logic power supply.
The signal BLCD_ENBA switches the backlight on or off.
The user can define the backlight active time in the configuration menu.
2.3.8 Keypad interface
The keypad interface contains the control register for 8 keypad columns and the receiving
register for 7 keypad rows, and the control signals for the status LEDs: LED_LIN,
LED_BATT, LED_START and LED_STOP.
Using the matrix of 8 x 7, up to 56 keypads can be detected.
Identification of the key pressed is as follows:
The controller activates a column, activation is via low-level, then the row-register is read to
identify the pressed key by a low-level. This procedure is repeated with the next column, till
all columns have been activated.
2.3.9 Printhead control
The printhead controller takes on the complete control of the 216-mm thermal printhead
with a line width of 200 mm.
The output rate to the printhead is 1000 /sec. The resolution in the Y-direction is 8 dot/mm,
in the X- time axis up to 40 dots/mm.