Z85C3008PEG Datasheet, PDF (36/81 Pages) Zilog, Inc. – CMOS SCC Serial Communications Controller

CMOS SCC Serial Communications Controller
Product Specification
28
Data
1
1
0
0
1
0
NRZ
NRZI
FM1
FM0
Manchester
Figure 12. Data Encoding Methods
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
PS011706-0511
Functional Descriptions