UM0934 Datasheet, PDF (42/113 Pages) STMicroelectronics – ST7570 S-FSK power line networking System-on-Chip

Host interface
UM0934
Acknowledgement messages
After receiving a local frame on the host interface, both the external host and ST7570 must
send an acknowledgement or not acknowledgement message through either TXD (ST7570)
or RXD (external host).
The two messages have the same format for both ST7570 and the external host and they
are 1 byte long.
Table 13 lists their fixed codes.
Table 13. ACK and NAK message codes
Symbol
Definition
ACK
Acknowledgement
NAK
Not acknowledgement
Code
06h
15h
5.2.2
Local port arbitration rules
The ST7570 modem is always the communication master. In the case of no local transfer,
the ST7570 can initiate a local communication without taking into account the external host
status. On the other hand, when the external host wants to send data (using a local frame),
it must first send a request through the T_REQ (transmitting request) input port. Then, the
ST7570 answers with a status message allowing or not the reception of a frame (or any
other command).
Frame delimitation
Data coming from the UART serial port are an asynchronous flow of bytes. In order to divide
the byte flow into a frame flow, the ST7570 communication protocol uses two methods:
length and timeout.
When the number of bytes received reaches the expected frame length, in accordance with
the frame type characteristics, the frame reception ends.
The time interval between two consecutive characters (two local frames including start and
stop bits) in a local frame must not exceed T_IC (timeout inter-character): the receiving part
(ST7570 host interface or external host) no longer accepts any character after this delay
expiration.
Figure 16. Timeout inter-character TIC
Ch aract er
TIC
Character
The timeout inter-character (T_IC) is set by default at 10 ms after a reset and can be modified
by writing a dedicated MIB object (Section 6.5.12).
If the length and the checksum are both correct, the received frame is accepted, otherwise
all previous characters are discarded.
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Doc ID 17389 Rev 2