Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 122)

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(n-2) Wait for OK.
(n-1) Send AT&T6 to the modem.
(n) Wait for OK.
5.8.2. Method 2
Send the entire file using a program that waits for OK after every line. This will require 3.98 seconds for a 6235 byte
patch at 115 kbaud or longer if the OS has latency.
5.8.3. Method 3
For development purposes, send the entire patch file using a program that allows a timed preprogrammed pause
between lines, e.g. HyperTerminal or ProComm. This will give times of around 16 seconds for a 6235 byte patch (at
115 kbaud). Due to the granularity of a typical desktop operating system, be sure to set the time delay between
lines to 100 ms.
A CRC can be run on the upgrade file loaded into on-chip Program RAM with the AT&T6 command to verify that
the upgrade was correctly written to the on-chip memory. The CRC value obtained from executing the AT&T6
command should match the CRC value provided with the upgrade code.
5.9. Escape Methods
There are four ways to escape from data mode and return to command mode once a connection is established.
Three of these, +++, “9th Bit”, and the “Escape Pin”, allow the connection to be maintained while one or both
modems are in the command mode. The fourth method is to terminate the connection. The three escape methods
that maintain the connection are combined by a logical OR. For example, if +++ and the “Escape Pin” are both
enabled, either returns the modem to the command mode from the data mode. In parallel or SPI mode, the escape
pin is not available. Instead the system can set the ESC flag in Hardware Interface Register 1 (HIR1).
While in data mode, an escape to command mode occurs if an escape command is sampled as negated for at
least 60 ms, then sampled asserted for at least 60 ms. The modem is then prepared to accept AT commands,
regardless of whether OK has been sent to the host. If the modem is already in command mode, the modem does
not send OK. The host should always wait for OK before entering the next command after an escape.
When making a new connection, the host must not try to escape between the connect message and the protocol
message. An escape attempt in this interval may fail because the modem is not in data mode until after the
protocol message. In practice, it is difficult to determine the exact boundary between command mode and data
mode. The recommendation is to time the escape command 100 ms low and 100 ms high, and expect that the
modem has transitioned to command mode.
Table 82. Load Technique and Speed Table*
Start Condition Delay
Between
Lines
Load time, 6235-Byte
Patch, 115 kbaud UART
Approach Used With
Reset, then
ATE0 and ATQ1
0.5 ms 0.694 Embedded systems
1 ms 0.771 Embedded systems
2 ms 0.925 Embedded systems
5 ms 1.385 Embedded systems
10 ms 2.152 Embedded systems
Reset Wait for OK 3.998 Windows or embedded system where
time precision is worse than 10 ms
Reset 100 ms 15.962 Windows without writing a patch loader
*Note: The delay times do not include the time to empty the UART's possibly long TX buffer. The time quoted is between the
end of transmission of the last character of a line and the start of transmission of the first character of the next line.