User`s manual

58 PCL-848AB User's Manual
7. TBEORY OP OPERATION
7.1. Introduction
This section describes the operation theory of this IEEE-488 t interface card. A
thorough understanding of the theory will increase its usefulness and help avoid future
problems.
7.2. Block Diagram Description
Figure 7.1. is the block diagram of this interface card. The i interface transfers data in a
bi-directional fashion between the PC-Bus and the IEEE-488 instrument bus. The
IEEE-488 bus driver is stored in the on-board ROM. When the application program
calls the bus driver, the driver routines generates the necessary bus command sequence
and then transparently passes the data ~ string to or from the bus device.
All of the major elements of this card are interconnected by the data bus of the PC
bus.
When an IEEE-488 bus driver routine is called, the CPU starts the t routine stored in
the ROM. The driver routine controls the IEEE-488 INTERFACE CONTROLLER to
execute the necessary command E sequence.
The on-board RAM is for the storage of the interface parameters, such as the IEEE-
488 address of the controller. The IEEE-488 INTERFACE CONTROLLER is an IC
chip which provides an interface ; between a microprocessor system and the IEEE-
488 interface bus. This IC is controlled and configured through 8-bit I/O mapped
registers and enables all aspects of the IEEE-488 standard to be implemented,
including talker, listener and controller functions.
When the computer executes a data output from the PC to a bus device, the driver
routine writes the data byte to the IEEE-488 interface controller chip and the chip will
handshake the byte out to the bus via the IEEE-488 bus driver/receiver. When entering
data from a bus device, the driver routine sets the IEEE-488 interface controller chip
to accept data and waits for . the handshake to be completed. The data byte is
received via the bus driver/receiver and then is put into the system memory.