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Z80 CPU Peripherals

User Manual

UM008101-0601 Serial Input/Output

273

characteristics of the channels. With the exception of WR0, programming

the write registers requires two bytes. The first byte contains three bits (D2-

D0) that point to the selected register; the second byte is the actual control

word that is written into the register to configure the Z80 SIO.

After pointing to the selected register, a programmer can either read to test

the read register or write to initialize the write register. The Z80 SIO

software can be initialized in either a modular or structured mode, allowing

the programmer to use powerful block I/O instructions.

WR0 functions as a unique register because all the basic commands

(CM02-CMDO) can be accessed with a single byte. Reset (internal or

external) initializes the pointer bits D0-D2 to point to WR0.

The basic commands (CMD2-CMD0) and the CRC controls (CRC0,

CRC1) are contained in the first byte of any write register access. This

allows maximum flexibility and system control. Each channel contains

the following control registers. These registers are addressed as

commands, not data.

Write Register 0

WR0, (Figure 114) is the command register; however, it is also used for

CRC reset codes and points to the other registers.

Table12.WriteRegister0

D7 D6 D5 D4 D3 D2 D1 DO

CRC CRC CMD CMD CMD PTR PTR PTR

ResetReset210210

Code Code

1 2 ... 288 289 290 291 292 293 294 295 296 297 298 ... 329 330

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