Service manual

CPU Assembly
3-7
NVRAM Interface
The NVRAM contains 1K bits of non-volatile storage for the cardiograph configuration.
Keyboard Interface
The passive Keyboard is scanned by the System Gate Array for keypresses. The LED(s)
are also driven by the System Gate Array. The software is responsible for determining
which keyboard is loaded and configuring the instrument for proper operation.
Display Control for PageWriter 20 and 300 Series
The display is a 240 x 128 dot super-twisted nematic Liquid Crystal Display module with
integrated driver circuitry. Its operation is controlled by the System Gate Array.
NVRAM
The NVRAM stores configuration information. It is written to by the System Gate Array
under software control and requires no power to retain its data.
ECG Front End
The ECG Front end is described in “ECG Front End”.
DRAM
The DRAM (Dynamic Random Access Memory) is a 256K x 16 bit read/write memory.
The System Gate Array provides the multiplexed address information, generates RAS and
CAS, and provides the timing and control required for memory transfers from and to the
CPU. The DRAM connects directly to the Data bus.
ROM-1 and ROM-2 Address Space
Cardiographs with serial number prefix CNA, CNB, CNC, or 3807A or earlier have a
Control Board with space for two ROMs (Read Only Memory) to provide data and
instructions for the CPU. In addition, the Control Board expansion connector and System
Gate Array provide for additional expansion. Each ROM contains 512K x 16 bits of read-
only memory.
Cardiographs with serial # prefix CND have one 2MB EPROM on the control board
which defines the ROM1 and ROM2 address spaces. The ROM contains 2MB x 16 bits of
read-only memory.
Printer Gate Array/SRAM
The printer gate array is the principal component of the printer control circuitry. It buffers
print data from the system, and status data going to the system. It also controls printer