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SERIAL I/O INTERFACE
The Am96/4116A has two RS232C serial ports.
Both channels can be
prograrruned
to
operate
with
either
synchronous
or
asynchronous
protocol s. Character 1ength, number of stop bi ts, and even/odd pa ri ty
are program selectable.
The Serial I/O Interface consists primarily of
two 9551 Programmable Communications Interface devices, part of an
Am9513 System Timing ControlOler used as a baud rate generator, and
dri veri recei ver ci rcui ts.
The fo 11 owi ng descri pt i on wi 11 be on one
Am9551.
Any exceptions will be noted.
Address bit 1 (AB1) is applied
to the C/O input of the Am9551.
An output instruction (serial 2 CE*,
10 WR ITEl *, and C/O high) causes the Am9551 to accept a cont ro 1 byte
through its data bus pi ns.
The control byte can be either a mode
i nst ruct i on or a command i nst ruct ion, dependi ng on the sequence in
which it is sent.
The mode instruction specifies the baud rate
multiplier, character length, parity, and the number of stop bits.
The
actua 1 baud rate select ion is determi ned by the baud rate input from
the Am9513.
The command word instructs the Am9551 to enable/disable
the receiver and transmitter, to reset errors, to return to Idle mode,
and to set/clear the Data Terminal Ready Signal output.
An output
instruct ion al so causes the Am9551 to accept a data byte through its
data bus pins.
Bit 0 is the least significant bit and bit 7 is the
most significant bit.
The 1\rn9551 will subsequently transmit serial
data to an external device if the transmitter is enabled.
An input instruction (Serial 2 CE*, 10 REAO*, and C/O high) causes the
Am9551 to place a status byte on the data bus.
The status bits are the
resul t of status and error check i ng funct ions performed wi thi n the
Am9551.
An input instruction al so causes the Am9551 to output a data
byte onto the data bus.
Bit 0 is the least significant bit and bit 7
is the most significant bit.
Timing for the Am9551 internal functions is provided by a 2.4576
MHz
output
from
counter
U40,
which
is
derived
from
a 19.6608
MHz
oscillator.
The Am9513 also uses the 2.4576
MHz
signal.
Jumpers at
the Am9513 determi ne the baud rate source.
The baud rate can be
jumpered for 9600 baud, which is from the Am9513 FOUT pin or for
programmable baud rates from counters 3 and 4 in the Am9513.
The clock
source for Serial Port 1 can also be from external sources.
The clock
source for Serial Port 2 is the on-board source only.
A hi gh on the Am9551 RESET 1 i ne forces the devi ce into an ; dl e mode.
After a hi gh RESET input, the Am9551 rema i ns i d 1 e unt i 1 a new set of
control words are written into the Am9551 to define its function.
In addition to the above control lines, the Am9551 also has a set of
control inputs and outputs that can be used to simpl i fy the interface
to almost any serial data device.
These control signals are general
purpose in nature.
The following paragraphs describe the interface
controls.
Receiver Data (RxO)
Serial data is received from the communication
line of the RxO input.
4-6
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