UM2241
Host interface
DocID030767 Rev 1
9/26
Bit
Name
MIB index
Description
6
Manufacturer data
6
Physical address (ACA) of the modem and serial number
7
Reserved
-
-
8
Reserved
-
-
9
Reserved
-
-
10
Reserved
-
-
11
Reserved
-
-
12
Reserved
-
-
13
Reserved
-
-
14
Reserved
-
-
15
Reserved
-
-
1.6
TREQ management
Here below a timing diagram of the priority negotiation of the serial link is depicted, first of
all the host controller wanting to send a command to the ST75MM drives low the TREQ
line, waiting for the SM frame before sending the message.
As soon as the SM frame starts, the host controller drives high the TREQ line and, when
the SM is completely received, it verifies that PLC Busy flag is disabled.
If the PLC Busy flag of the SM is disabled the host controller sends the command to the
ST75MM within T
SR
time, and waits for a maximum of T
ACK
time the acknowledge byte from
the ST75MM.
If the acknowledge byte is not received within T
ACK
time, the host controller can initiate a
new transaction, sending the same command with 0x03 as start of the frame byte, this way,
if the acknowledge byte has been lost in the serial link the ST75MM receives the command
twice and can disregard the repetition.
Figure 2: TREQ negotiation timing diagram
1.7
Examples
Here below an example of DL_DATA_SLAVE.indication coming from the ST75MM, in this
case, as in MIB_Write.indication, being the message triggered by the ST75MM there is no
negotiation with the host controller in the serial link.
