Service manual

CPU Assembly
3-5
CPU/System Oscillator
The CPU (Central Processing Unit) is the processing engine for the instrument. The
microprocessor used is the Intel 80960SA, a 32 bit microprocessor with a 32-bit address
bus and a 16-bit external data bus (32 bit internal data bus). The lower 16 bits of the
address bus are multiplexed with the data bus; these lines are de-multiplexed by the
System Gate Array. The processor operates at 16 MHz off of a 32 MHz System Oscillator.
The data and address buses are shown in the above block diagram.
Instructions for the CPU are stored in RAM and ROM external to the CPU.
System Gate Array/Real-Time Crystal
The System Gate Array provides the following functions:
• ECG Front End control
• Interrupt control
• DMA for ECG data
• DMA for LCD data
• System reset circuitry
• Watch-dog circuitry
• Real-time clock (including driving the external Real-Time crystal)
• DRAM RAS and CAS generation and refresh
• Interface to the Serial EEROM
• Address decoding for the Printer Gate Array and ROMs
• Keyboard scan and LED drive
• LCD control (for the PageWriter 200/300 series)
ECG Front End Control
The ECG Front End control interface consists of serial command data to the front end, and
serial data (ECG or status) from the front end.
The input command data consists of a single 24-bit word containing an address field and a
control field. Depending on the data in the address field, the contents of the control field
apply to either
• configuring each individual front end integrated circuit,
• configuring both front end integrated circuits together as a system, or
• setting the calibration value of the front end integrated circuit
Interrupt Control
The interrupt control interface manages two of the four processor interrupt signals. The
processor interrupt signal names are nINT0, INT1, INT2, and nINT3. nINT0 and nINT3
are controlled by the System Gate Array. INT1 is for interrupts from an expansion board
(such as the Option #A05 storage and transmission board) connected to the System
Expansion Connector. INT2 is controlled by the Printer Gate Array.