AMIS-49587 Datasheet, PDF (18/59 Pages) ON Semiconductor – Power Line Carrier Modem

AMIS−49587
(PRE_SLOT )
IO2
AMIS −49587
TxD
RxD
T_REQ
TxD
RxD
Base Micro
Figure 14. Connection to the Application Microcontroller
SCI 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 base micro.
RXD: Receive data input. It is the data input of the
AMIS−49587 and the output of the base micro.
BR0, BR1: Baud rate selection inputs. These pins are
externally strapped to a value or controlled by the external
base microcontroller.
Table 24. BR1, BR0 BAUD RATES
BR_1
BR_0
0
0
0
1
1
0
1
1
Baud rate
4800 baud
9600 baud
19200 baud
38400 baud
Arbitration and Transfer
In order to avoid collisions between the data sent by the
AMIS−49587 and the base micro, 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 base
micro state. In the other hand, when the base micro 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 that contains information
about the possibility of receiving a MA_Data_Request
encapsulated in a local frame. The AMIS−49587 is the
communication controller and has priority in a
communication. This means that as soon as the
AMIS−49587 wants to send a local frame (e.g. a local frame
including a MA_Data_Indication), if the local
communication channel is available (no local transfer has
already begun), it can send this local frame.
If the status message indicates a PLC buffer unavailable
when the base micro wants to send a MA_Data_Request
encapsulated in a local frame, this local frame will be
answered by a Confirm « Resource Unavailable » if the base
micro insists to send it.
Transfer from Base Micro to AMIS−49587
When the base micro wants to initiate a local transfer, it
must pull down the T_REQ signal. The AMIS−49587
answers within the Tpoll delay with the status message in
which the base micro can read if the communication channel
is available.
If the communication is possible, the base micro can start
to send its local frame within the Tsr 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 Tsr delay was issued, the AMIS−49587 ignores
the local frame.
Remark: If the base micro 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.
At the end of the data reception sent by the base micro 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
or NAK).
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