DS232-4 June ’04

©2004 Reg. No. 227 4001, ENGLAND

Page 5

232C-868FR1

2

Software Specifications

2.1

Operating modes

The RF modem is able to operate in four different modes which can be configured by setting register

values using AT commands. Sections 2.2 - 2.4 give a full explanation of how to program the registers,

the operation of the different modes is explained in detail in the following paragraphs.

2.1.1

Transparent Mode

In Transparent Mode, the RF modem behaves like a wired serial link, i.e. the modem does not only

transmit to the radio channel every data received on the serial link, but also transmits on the serial link

the information received on the radio channel.

Basically the RF modem reproduces the half-duplex function of a RS-485 cable.

There is no flow control performed by the modem in the transparent mode, neither on the serial link nor

on the radio link. Flow control must be carried out by software applications via various protocols in use

such as MODBUS, JBUS, etc…

Consequently, in Transparent Mode it is not possible to change the modems parameters without a

temporary return to Hayes mode.

NOTE: The user’s software application must adequately verify that all buffers are transmitted correctly

taking into account that an interrupted transmission link may lead to losing one or several buffers.

2.1.2

Transparent Secured Mode

In order to confirm the correctness of the transmitted data frames, data flow control between the

modems is added to the Transparent Mode, so that each data transfer is “data verified”. This mode shall

be operated for point-to-point communications only.

Transparent Secured Mode or Transparent «Data Verified» Mode’s purpose is to offer an optimal radio

link quality and to provide transparent mode with the necessary security in case flow control would not

be included within the user’s application software.

The risk of data loss is much lower than during the use of application software only because this latter is

dependent on the intermediate times inserted by the serial link.

Moreover, a flow control is performed on the serial link in order to warn the user that the buffer (including

132 characters) is saturating. The warning level is default set to 132 characters and can be programmed

via register S218.

NOTE: The user’s software application must adequately verify that all buffers are transmitted correctly

taking into account that an interrupted transmission link may lead to losing one or several buffers. After

N Time repetition of a buffer (N programmable up to 255 with S223) without a correct acknowledgement

the buffer shall be considered as lost.

2.1.2.1

«Secured» link Algorithm

The transmitting modem proceeds to data framing:

•

Transferred Data Count up.

•

Transferred Data Frame Type.

•

Frame number.

•

Data to be transmitted.

•

16 bits Checksum.

The receiving modem analyses this data frame and checks its consistency.

When the data frame is received correctly, the receiver transmits an acknowledgement back to the

transmitter, and delivers the received data framing to its serial link.

In case the reception is not without errors, the receiver requests a new framing transmission to the

transmitter. The number of repetitions depends on the parameter programmed in the modem

configuration (Register S223).

At serial port level, each transmitted data frame is «Data Verified», but no statement asserts to the user

whether the data frame has been transmitted yet or not.