Z80181 Datasheet, PDF (7/74 Pages) Zilog, Inc. – SMART ACCESS CONTROLLER (SAC™)

Zilog
SCC SIGNALS
Pin Name
/W//REQ
Pin Number
51
Input/Output, Tri-State
Active 0
/SYNC
50
I/O, Active 0
RxD
52
/RTxC
49
In, Active 1
In, Active 0
/TRxC
53
I/O, Active 0
Z80181
SMART ACCESS CONTROLLER SAC^™
Function
Wait/Request. Open-drain when programmed for a Wait
function, driven “1” or “0” when programming for a Re-
quest function. Used as /WAIT or /REQUEST depending
upon SCC programming. When programmed as /WAIT,
this signal is asserted to alert the CPU that addressed
memory or I/O devices are not ready and that the CPU
should wait. When programmed as /REQUEST, this signal
is asserted when a peripheral device associated with a
DMA port is ready to read/write data. After reset, this pin
becomes “/WAIT”.
Synchronization. This pin can act either as input, output,
or part of the crystal oscillator circuit. In asynchronous
receive mode (crystal oscillator option not selected), this
pin is an input similar to /CTS and /DCD. In this mode,
transitions on this line affect the state of the Sync/Hunt
status bit in Read Register 0 but has no other function.
In external sync mode with crystal oscillator option not
selected, this line also acts as an input. In this mode,
/SYNC must be driven “0” two receive clock cycles after
the last bit in the synchronous character is received.
Character assembly begins on the rising edge of the
receive clock immediately preceding the activation
of /SYNC.
In internal sync mode (Monosync and Bisync) with the
crystal oscillator option not selected, this line acts as
output and is active only during the part of the receive clock
cycle in which a synchronous character is recognized
(regardless of character boundaries). In SDLC mode, this
pin acts as an output and is valid on receipt of a flag.
Receive Data. This input signal receives serial data at
standard TTL levels.
Receive/Transmit Clock. This pin can be programmed in
several different modes of operation. /RTxC may supply
the receive clock, the transmit clock, the clock for the Baud
Rate Generator, or the clock for the Digital Phase-Locked
Loop. This pin can also be programmed for use with the
/SYNC pin as a crystal oscillator. The receive clocks can be
1, 16, 32, or 64 times the data transfer rate in Asynchronous
mode.
Transmit/Receive Clock. This pin can be programmed in
several different modes of operation. /TRxC can supply the
receive clock or the transmit clock in the input mode. Also,
it can supply the output of the Digital Phase-Locked Loop,
the crystal oscillator, the Baud Rate Generator, or the
transmit clock in the output mode.
DS971800500
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