Z8523016VEG Datasheet, PDF (107/118 Pages) Zilog, Inc. – Enhanced Serial Communications Controller

Z80230/Z85230/L
Product Specification
102
2. Enable the CRC/Flag on Underrun (WR10 bit 2 equals 0).
3. Issue a Deactivate RTS command in the Transmit Underrun ISR. The RTS signal
deactivates automatically after the closing flag disappears.
The Automatic RTS Deactivation command works for a single frame and for two
consecutive frames back-to-back. This command does not work with more than two back-
to-back frames.
In the latter condition, if the Deactivate RTS command is issued at the beginning of the
Transmit Underrun ISR. RTS is deactivated after the CRC is gone, but before the clos-
ing flag is sent. The final frame is not concluded, and is corrupted.
RTS Problem Solutions
A workaround for the RTS problem is not to send back-to-back frames. Idle time is
inserted between frames.
There is, however, a limitation to this workaround in that the system throughput is reduced
by the idle time inserted between the frames.
Figure 36 displays Automatic RTS Deactivation.
RTS
Frame n-1
Frame n
TxD
Flag Frame n-1 CRC Flag Frame n CRC Flag
RTS deactivates correctly (after the closing flag)
if only one back-to-back frame is sent.
RTS
TxD
Frame n-1
Frame n
Flag Frame n-1 CRC Flag Frame n CRC Flag
RTS must deactivate
after the last closing
flag is gone.
RTS deactivates too soon, after the CRC, but before the closing
flag if more than two back-to-back frames are sent.
Figure 36. Automatic RTS Deactivation
Automatic TxD Forced High Problem Description
If WR10 is programmed with bits 6 and 5 equal to 01 (NRZI), bit 3 equals 1 (Mark Idle)
and WR4 bits 5 and 4 equal 10 (SDLC), the TxD pin is forced High after detecting the last
bit of the closing flag at the falling edge of TxC. This feature does not work if back-to-
PS005308-0609
Z80230/Z85230/L Errata