Silicon Laboratories SI2493/57/34/15/04, SI2494/39 Escape Methods, Load Technique and Speed Table

AN93

(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.

Table 82. Load Technique and Speed Table*

Start Condition	Delay	Load time, 6235-Byte	Approach Used With
	Between	Patch, 115 kbaud UART
	Lines
Reset, then	0.5 ms	0.694	Embedded systems
ATE0 and ATQ1
	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.

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.

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