Z8523L08VEG Datasheet, PDF (26/118 Pages) Zilog, Inc. – Enhanced Serial Communications Controller

Z80230/Z85230/L
Product Specification
21
Table 3. Data Encoding Descriptions (Continued)
Code Type
Level
Value
FM1 (biphase mark) Additional Transition at the Center of the Bit Cell 1
No Additional Transition at the Center of the Bit 0
Cell
FM0 (biphase
space)
A transition occurs at the beginning of every bit 0
call. A 0 is represented by an additional transition
at the center of the bit cell.
A 1 is represented by no additional transition at 1
the center of the bit cell.
In addition to the four methods, ESCC can be used to decode Manchester (biphase level)
data using DPLL in the FM mode and programming the receiver for NRZ data. Man-
chester 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 ESCC is capable of automatically echoing everything it receives. This feature is use-
ful mainly in ASYNCHRONOUS modes, but works in SYNCHRONOUS and SDLC
modes as well. AUTO ECHO mode (TxD is RxD) is used with NRZI or FM encoding
with an 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 transi-
tions for this input can cause interrupts if programmed to do so). In this mode, the trans-
mitter is actually bypassed and the programmer is responsible for disabling transmitter
interrupts and Wait/Request on transmit.
The ESCC is also capable of LOCAL LOOPBACK. In this mode the internal transmit
data is tied to the internal receive data and RxD is ignored. The CTS and DCD inputs are
also ignored as transmit and receive enables. However, transitions on these inputs can
cause interrupts. LOCAL LOOPBACK works in ASYNCHRONOUS, SYNCHRO-
NOUS, and SDLC modes with NRZ, NRZI, or FM coding of the data stream.
PS005308-0609
Functional Description