Z80382 Datasheet, PDF (58/77 Pages) Zilog, Inc. – HIGH-PERFORMANCE DATA COMMUNICATIONS PROCESSORS

Z80382/Z8L382
High-Performance Data Communications Processors
Zilog
SERIAL COMMUNICATION CHANNELS (Continued)
Start of Transmission: The first byte of data is placed on
the bus and MX is activated (Low). MX remains active, and
the data is repeated until an inactive-to-active transition of
MR is received, indicating that the data has been captured
by the receiver.
Subsequent Transmissions: The second and subse-
quent bytes are placed on the bus after the inactive to ac-
tive transition of MR. At the time that the second byte is
transmitted, MX is returned inactive for one frame time
only; the data is valid in the same frame. In the following
frame, MX returns active again and the same byte is trans-
mitted. Data is repeated in subsequent frames and MX re-
mains active until acknowledgment is detected (MR transi-
tion from inactive to active).
Maximum Speed Case: The transmitter is capable of min-
imizing the delay between bytes to achieve higher data
throughput than is provided by the general case described
above. The first and second bytes are transmitted normal-
ly, However, starting with the third byte, the transmitter will
deactivate MX and transmit new data one frame time after
MR is deactivated. In this way, the transmitter is anticipat-
ing that MR will be reactivated, which it will do one frame
time after it is deactivated, unless an abort is signalled by
the receiver.
Reception: At the time the receiver sees the first byte, in-
dicated by the inactive-to-active transition of MX, MR is by
definition inactive. In response to the activation of MX, the
data is read off the bus and MR is activated. MR remains
active until the next byte is received or an end of message
is detected. Subsequent data is received from the bus on
each falling edge of MX, and a monitor channel receive
data available interrupt is generated. Note that the data
may actually be valid at the time that MX went inactive, one
frame time prior to going active. MR is deactivated after the
data is read and reactivated one frame time later. The
transmitter will detect MR going inactive and anticipate its
reactivation one frame later. The reception of data is termi-
nated by the reception of an end of message indication.
Abort: The abort is a signal from the receiver to the trans-
mitter indicating that the data has been missed. It is not an
abort in the classical sense, which is an indication that the
current message should be ignored. The receiver indi-
cates an abort by holding MR inactive for two or more
frames in response to MX going inactive.
Flow Control: The receiver can hold off the transmitter by
keeping MR active until the receiver is ready for the next
byte. The transmitter will not start the next transmission cy-
cle until MR goes inactive.
End of Message (EOM): The transmitter sends an EOM,
normally after the last byte of data has been transmitted,
by not reactivating MX after deactivating it in response to
MR going inactive.
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PRELIMINARY
DS97Z382000