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UM008101-0601 Serial Input/Output

272

PROGRAMMING

Overview

To program the Z80 SIO, the system program first issues a series of

commands that initialize the basic mode of operation and then other

commands that qualify conditions within the selected mode. For example,

the Asynchronous mode, character length, clock rate, number of stop bits,

even or odd parity are first set, then the interrupt mode and, finally, receiver

or transmitter enable. The WR4 parameters must be issued before any other

parameters are issued in the initialization routine.

Both channels contain command registers that must be programmed via the

system program prior to operation.

The Channel Select input (B/A

) and the Control/Data input (C/D)arethe

command structure addressing controls, and are normally controlled by the

CPU address bus (see Table 11). Figures 114 through 117 illustrate the

timing relationships for programming the write registers, and transferring

data and status.

Write Registers

The Z80 SIO contains eight registers (WR7-WR0) in each channel that are

programmed separately by the system program to configure the functional

Table 11. Channel Select Functions

C/D

B/A Function

00ChannelAData

01ChannelBData

1 0 Channel A Commands/Status

1 1 Channel B Commands/Status

1 2 ... 287 288 289 290 291 292 293 294 295 296 297 ... 329 330

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Zilog Z08470 Manual de usuario Pagina 292