z85c30 ZiLOG Semiconductor, z85c30 Datasheet - Page 28

• Manufacturer Part Number: z85c30
• Description: Cmos Scc Serial Communications Controller
• Manufacturer: ZiLOG Semiconductor

PS011705-0608
Data Encoding
The SCC can be programmed to encode and decode the serial data in four different
methods (Figure 12). In NRZ encoding, a 1 is represented by a High level and a 0 is
represented by a Low level. In NRZI encoding, a 1 is represented by no change in level
and a 0 is represented by a change in level.
In FM1 (more properly, bi-phase mark), a transition occurs at the beginning of every bit
cell. A 1 is represented by an additional transition at the center of the bit cell and a 0 is
represented by no additional transition at the center of the bit cell.
In FM0 (bi-phase space), a transition occurs at the beginning of every bit cell. A 0 is
represented by an additional transition at the center of the bit cell, and a 1 is represented by
no additional transition at the center of the bit cell.
In addition to these four methods, the SCC can be used to decode Manchester (bi-phase
level) data by using the DPLL in the FM mode and programming the receiver for NRZ
data. Manchester encoding always produces a transition at the center of the bit cell. If the
transition is 0 to 1, the bit is a 0. If the transition is 1 to 0, the bit is a 1.
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
Manchester
NRZI
Data
NRZ
FM1
FM0
Figure 12. Data Encoding Methods
1
1
CMOS SCC Serial Communications Controller
0
0
1
0
Product Specification
Functional Description
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