ICS ELECTRONICS 4863 Manual page 116

4
Theory of Operation
4.1 INTRODUCTION
This section describes the theory of operation of the 4863 and 2363.
4.2 BLOCK DIAGRAM DESCRIPTION
A block diagram of the 4863 is shown in Figure 4-1. The 4863 is a
microprocessor based device that accepts commands from the GPIB (IEEE
488) bus to control its relay outputs and to read digital inputs. The 4863 is
made up of nine major elements, most of which are interconnected to the
microprocessor by a common data, address and control signal bus.
Incoming GPIB bus data and commands are received by the GPIB controller
chip. Each received character interrupts the microprocessor to accept GPIB
command and data characters When the command terminator is sensed, the
command characters are parsed and used to charge the 4863's operational
settings or invoke some action or response. The typical action for the Model
4863 is to transfer data from the GPIB or Serial interfaces to/from the digital
I/O latches.
The 4863's digital input circuits are designed to accommodate contact
closures, TTL logic inputs or CMOS logic inputs. Each of the 48 digital
inputs has a 33 Kohm pullup resistor to +5 Vdc. The Status inputs and the
EDR input are HCT type inputs.
The Flash memory contains all of the 4863's program instructions, command
tables, and power turn-on/self test routines. At power turn-on, the 4863
performs a self test on each functional block to determine whether there is
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