Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 299)

AN93
Rev. 1.3 299
The infinite loop has two functions depending on the use of interrupts or polling for modem communication:
1. In interrupt mode, the TXE (modem) and TI0 (UART) interrupts are always jump-started by making periodic
calls to modemCommunicationUpdate() and to UARTCommunicationUpdate(), respectively. The calls
are necessary only to jump-start the modem and UART transmit interrupts. A system that is aware of the
transmit activity for both the modem and the UART can reduce the number of calls, thereby freeing MCU
bandwidth for other tasks.
2. In polling mode, only TI0 (UART) interrupts need jump-starting using periodic calls to
UARTCommunicationUpdate() , and repeated calls to modemCommunicationUpdate() are necessary to
poll the modem's HIR1 and determine the status of the transmit and receive FIFOs. An obvious limitation of the
polling method is the need to constantly poll the modem for a change of FIFO state, which uses up MCU
bandwidth.
Compiler Option: Dot Commands
To include diagnostic (dot command) functions, define DIAGNOSTICS by removing the comment slashes (//) at
the appropriate line in the modem_80C51.h header file, and include the files dot_command_loop.c and
test_code.c
in the project build. Contact Silicon Labs for more details on diagnostic commands.
Modem Operation
Initialization
After reset, the ISOmodem does not by default have all the required features enabled. When using the parallel or
SPI mode, Silicon Labs recommends the following initialization steps:
1. Push the command AT:U70,8F00 followed by carriage return into the transmit buffer. The setting of U70 can
vary, but it is recommended that bit 15 (HES) be set to enable escape.
2. Monitor the receive buffer for OK, indicating that the command was successful.
3. If a firmware upgrade needs to be programmed into the part, push the upgrade into the transmit buffer one line
at a time. The OK prompt must be received after each line.
4. Once the patch is written to the ISOmodem, other commands can be pushed into the transmit buffer.
5. If software interrupts are required, enable them by calling:
setControl( SiINTM, ENABLE, NOW ).
Silicon Labs also recommends the use of any firmware upgrade (provided by Silicon Labs) if called for in the errata
for that revision. Firmware upgrades address known problems with a given revision.
Making a Connection
Making a connection in parallel or SPI mode is no different than in UART mode. The application layer should keep
track of whether the ISOmodem is in command mode or data mode to determine whether to send an escape
before sending commands. The steps for making a connection are as follows:
1. Clear the HIR1 ESC bit by calling setControl( SiESC, DISABLE, NOW ).
2. Push the dial string into the transmit buffer, and begin monitoring for the CONNECT response.
3. The ISOmodem is now in data mode when the connect/protocol response is received.
4. The application layer can begin pushing data to the modem for transmission over the phone line. Received data
will accumulate in the receive buffer as a result of polling or interrupts.
Data Bursts
The ISOmodem has internal buffering of approximately one kilobyte in each of the receive and transmit directions.
The modem attempts to empty and fill these buffers as quickly as possible. This results in transmit and receive data
bursts at a much faster rate than the modem connection. The receive bursts are limited by the V.42 frame size and
the V.42bis data compression ratio. The higher the compression ratio, the longer the burst will be. The transmit
bursts can be as large as one kilobyte when transmission first begins. Once the buffer is full, the transmit bursts are
also limited by the V.42 frame size and compression ratio.