AMIS-49587_15 Datasheet, PDF (30/56 Pages) ON Semiconductor – Power Line Carrier Modem

AMIS−49587
6.4.3 Serial Communication Interface Physical Layer
Description
The following pins control the serial communication
interface.
TXD: Transmit data output.
It is the data output of the AMIS−49587 and the input of the
application micro controller.
RXD: Receive data input.
It is the data input of the AMIS−49587 and the output of the
application micro controller.
T_REQ:Transmit Request input
Request for data transmission received from the application
micro controller.
BR0, BR1: Baud rate selection inputs.
These pins are externally strapped to a value or controlled by
the external application micro controller.
Table 28. BR1, BR0 BAUD RATES
BR1
BR0
SCI Baud Rate
0
0
4800
0
1
9600
1
0
19200
1
1
38400
IDLE (mark)
LSB
MSB
IDLE (mark)
Start D0
D1 D2 D3
D4
D5
D6
D7 Stop
t_BIT
8 data bits
t_BIT
1 character
Figure 25. Data Format
6.4.4 Arbitration and Transfer
In order to avoid collisions between the data sent by the
AMIS−49587 and the application micro controller, the
AMIS−49587 is chosen as the transmitting controller. This
means that when there is no local transfer, the AMIS−49587
can initiate a local communication without taking account of
the application micro controller state. On the other hand,
when the application micro controller wants to send data
(using a local frame), it must first send a request for
communication through the local input port named T_REQ
(Transmitting Request). Then the AMIS−49587 answers
with a status message.
6.4.5 Transfer from Application Microcontroller to
AMIS−49587
When the application micro controller wants to initiate a
local transfer, it must pull down the T_REQ signal. The
AMIS−49587 answers within the t_POLL delay with the status
message in which the application micro controller can read
if the communication channel is available. If the
communication is possible, the application micro controller
can start to send its local frame within the t_SR delay. It should
pull up the T_REQ signal as soon as the first character (STX)
has been sent. If the beginning of the local frame is not
received before the t_SR delay was issued, the AMIS−49587
ignores the local frame. At the end of the data reception sent
by the application micro controller on the RxD line, the
AMIS−49587 sends a byte on the TxD line in order to inform
about the status of the transmitting <ACK> (=0x06) or
<NAK> (=0x15).
Remark: If the application micro controller only wants to
know the state of the AMIS−49587, it has just to pull up the
T_REQ signal after the reception of the status message.
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