Silicon Laboratories SI2493/57/34/15/04, SI2494/39 manual Chinese ePOS SMS, SMS Message Format

AN93

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.

			Data Frame
Channel Seizure	Mark Signal					Mark
Protocol 1: 0 bits	Protocol 1: 80 bits +/-25					Signal
Protocol 2: 300 bits	Protocol 2: 80 bits +/- 25
		Type	Length	Payload	Checksum

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.

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