Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 234)

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234 Rev. 1.3
9. Chinese ePOS SMS
9.1. Introduction
An ePOS transaction normally begins with the ePOS terminal calling the server and transmitting data first. In this
instance the terminal initiates the call, so it is known as the Originate modem, while the server is the Answer
modem. After the modems connect, go through handshake and complete the first data transmission, the two
modems alternate being the transmitter and receiver until the completion of the call.
The Si24xx ISOmodems support SMS (Short Message Service) in an ePOS (electronic point of sale) connection.
An SMS message is delivered in frames, using the format shown in Figure 37.
Figure 37. SMS Message Format
As shown in the figure, an SMS frame follows one of two protocols, Protocol 1 or Protocol 2. Protocol 1 frames
begin with the Mark signal, while Protocol 2 frames start with the Channel Seizure (CS) signal. Otherwise the two
protocols are identical. The Originate modem is configured to transmit in one of the two protocols at the beginning
of a call. The Answer modem recognizes which protocol is being sent and processes the incoming message
accordingly.
The modem strips off the Channel Seizure and Marks at the beginning and end of the data and provides the Data
Frame to the host processor.
It does not provide frame content verification of any kind.
Channel Seizure
Protocol 1: 0 bits
Protocol 2: 300 bits
Mark Signal
Protocol 1: 80 bits +/-25
Protocol 2: 80 bits +/- 25
Data Frame
Type Length Payload Checksum
Mark
Signal