Zilog Z16C35 - Manual (Page 74)

ISCC
User Manual
UM011002-0808
68
4.3.3 Transmitter/Receiver Synchronization
The ISCC contains a transmitter-to-receiver synchronization function that may be used to
guarantee that the character boundaries for the received and transmitted data are the same.
In this mode the receiver is in Hunt and the transmitter is idle, sending either all "1s"" or
all "0s". When the receiver recognizes a sync character, it leaves Hunt mode and one char-
acter time later the transmitter is enabled and begins sending sync characters. Beyond this
point the receiver and transmitter are again completely independent, except that the char-
acter boundaries are now aligned. This is shown in Figure 4-10.
Figure 4–25. Transmitter to Receiver Synchronization
There are several restrictions on the use of this feature in the ISCC. First, it will only work
with 6-bit, 8-bit or 16-bit sync characters, and the data character or eight bits with an 8-bit
or 16-bit sync character. Of course, the receive and transmit clocks must have the same
rate as well as the proper phase relationship.
A specific sequence of operations must be followed to synchronize the transmitter to the
receiver. Both the receiver and transmitter must have been initialized for operation in Syn-
chronous mode sometime in the past, although this initialization need not be redone each
time the transmitter is synchronized to the receiver. The transmitter is disabled by setting
bit D3 of WR5 to “0”. At this point the transmitter will send continuous “1s”. If it is
desired that continuous “0s” be transmitted, the Send Break bit (D4) in WR5 should be set
to “1”. The transmitter is now idling but must still be placed in the transmitter to receiver
synchronization mode.
This is accomplished by setting the Loop Mode bit (D1) in WR10 and then enabling the
transmitter by setting bit D3 to WR5 to “1”. At this point the processor should set the Go
Active on Poll bit (D4) in WR10. The final step is to force the receiver to search for sync
characters. If the receiver is currently disabled the receiver will enter Hunt mode when it is
Receiver Leaves Hunt
Sync
Sync
RxD
TxD
Sync Sync
Direction of message flow
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