Z80 datasheet(282/330 Pages) ZILOG

282 / 330 page

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7UGT /CPWCN

UM008101-0601

Serial Input/Output

262

In all modes, characters are sent with the least-significant bits first. This

requires right justification of data to be transmitted when the word length is

less than eight bits. If the word length is five bits or less, use the special

technique described in “Write Register 5” on page 289.

Because the number of bits/character can be changed on-the-fly, the data

field can be filled with any number of bits. When used in conjunction with

the Receiver Residue codes, the Z80 SIO can receive a message that has a

variable I-field and retransmit it exactly as received with no previous infor-

mation about the character structure of the I-field (if any). A change in the

number of bits does not affect the character being shifted out. Characters

are sent with the number of bits programmed at the time that the character

is loaded from the transmit buffer to the transmitter.

If the External/Status Interrupt Enable is set, transmitter conditions, such as

“startingtosendCRC characters,”“starting to send flag characters,” and CTS

changing state, cause interrupts, having a unique vector if Status Affects

Vector is set. All interrupts can be disabled for operation in a polled mode.

Table 9 describes the typical program steps that implement the half-duplex

SDLC Transmit mode.

Table 9. SDLC Transmit Mode

Function

Typical Program Steps

Comments

Initialize WR0

Channel Reset

Reset SIO

WR0

Pointer 2

WR2

Interrupt Vector

Channel B only

WR0

Pointer 3

WR3

Auto Enables

Transmitter sends data only after CTS is

detected

WR0

Pointer 4, Reset External/status

Interrupts

Z80 Datasheet(PDF) 282 Page - Zilog, Inc.

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