Z80185 Datasheet, PDF (58/95 Pages) Zilog, Inc. – SMART PERIPHERAL CONTROLLERS

Zilog
PRELIMINARY
Z80185/Z80195
SMART PERIPHERAL CONTROLLERS
A LocalTalk feature has been added in one EMSCC of the
Z80185, operating as follows:
If a certain set of register bits are set, RTS acts as a
LocalTalk Driver Enable output that operates as shown in
Figure 50. All of the following bits and fields must be
programmed exactly as shown to enable this mode:
WR4.3-2 = 00: sync modes
WR4.5-4 = 10: SDLC
WR5.1 = 0: no RTS
WR7'.2 = 1: auto RTS deactivation
WR10.3 = 1: mark idle
WR5.4 = 1: Send Break
When the first five conditions above are set (as for LocalTalk
operation), the WR5.4 bit is used as a Select LocalTalk
Driver Enable control bit, rather than the Send Break
command bit used in async mode.
Setting these register bits in this manner configures the
EMSCC Transmitter to send three Flags before a frame,
negating RTS during the first to create a coding violation,
when software writes the first character of a frame to the
TDR and TxFIFO. This mode also makes the Transmitter
ensure at least 16 bits of idle time between a closing Flag
and the end of frame interrupt. The RTS output is driven
active for one bit time at the start of the first of the three
Flags, then inactive for four bit times, then active again for
the duration of the opening Flags, the frame, and closing
Flag, plus 16 bit times thereafter.
There is one other difference in EMSCC operation when
this new mode is enabled. The setting of the TxIP bit, that
normally occurs after the last bit of the CRC is sent, is
delayed until the 16-bit Idle is sent and RTS is negated.
RTS
TxD
Flag
Flag
Flag
Frame
Flag
16-Bit Idle
Figure 67. EMSCC Transmitter Flag Commands
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