Z80C30 datasheet(36/81 Pages) ZILOG

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PS011706-0511

Functional Descriptions

CMOS SCC Serial Communications Controller

Product Specification

Auto Echo and Local Loopback

The SCC is capable of automatically echoing everything it receives. This feature is useful

mainly in Asynchronous modes, but works in Synchronous and SDLC modes as well.

Auto Echo mode (Tx0 is Rx0) is used with NRZI or FM encoding with no additional delay

because the data stream is not decoded before retransmission. In Auto Echo mode, the

CTS input is ignored as a transmitter enable (although transitions on this input can still

cause interrupts if programmed to do so). In this mode, the transmitter is actually bypassed

and the programmer is responsible for disabling transmitter interrupts and WAIT/

REQUEST on transmit.

The SCC is also capable of local loopback. In this mode, TxD or RxD is similar to Auto

Echo mode. However, in Local Loopback mode the internal transmit data is tied to the

internal receive data and RxD is ignored (except to be echoed out through TxD). The CTS

and DCD inputs are also ignored as transmit and receive enables. However, transitions on

these inputs can still cause interrupts. Local Loopback works in Asynchronous, Synchro-

nous and SDLC modes with NRZ, NRZI or FM coding of the data stream.

SDLC FIFO Frame Status FIFO Enhancement

The SCC’s ability to receive high speed back-to-back SDLC frames is maximized by a 10-

deep by 19-bit wide status FIFO. When enabled (through WR15, bit D2), it provides the

Figure 12. Data Encoding Methods

Data

NRZ

NRZI

FM1

FM0

Manchester

Z80C30 Datasheet(PDF) 36 Page - Zilog, Inc.