Z80 datasheet(285/330 Pages) ZILOG

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Z80 CPU Peripherals

User Manual

UM008101-0601

Serial Input/Output

265

SDLC Receive

Initialization

The system initializes the SDLC Receive mode using polynomial, receive

word length, and more. The flag characters must also be loaded in WR7

and the secondary address field loaded in WR6. The receiver is enabled

only after all the receive parameters have been set. After all this is

completed, the receiver is in the Hunt phase and remains in this phase

until the first flag is received. While in the SDLC mode, the receiver

never re-enters the Hunt phase, unless specifically instructed to do so by

the program. The WR4 parameters must be issued prior to the WR1,

WR3, WR5, WR6, and WR7 parameters.

Under program control, the receiver can enter the Address Search mode. If

the Address Search bit (WR1, D2) is set, a character following the flag

(first non-flag character) is compared to the programmed address in WR6

and the hardwired global address (1111 1111). If the SDLC frame address

field matches either address, data transfer begins.

Because the Z80 SIO is capable of matching only one address character,

extended address field recognition must be done by the CPU. In this

instance, the Z80 SIO transfers the additional address bytes to the CPU as if

they were data characters. If the CPU determines that the frame does not

have the correct address field, it can set the Hunt bit, and the Z80 SIO

suspends reception and searches for a new message headed by a flag.

Termination

Redefine Interrupt Modes

Terminate gracefully

Update Modem Control

Outputs

Disable Transmit Mode

Table 9. SDLC Transmit Mode (Continued)

Function

Typical Program Steps

Comments

Z80 Datasheet(PDF) 285 Page - Zilog, Inc.