UM0239 datasheet(26/44 Pages) STMICROELECTRONICS

26 / 44 page

Receive sessions

UM0239

26/44

Receive sessions

Click RX on the toolbar to open a receiving session and to display the Receive Monitor

dialog box shown in Figure 14.

Figure 14.

Receive Monitor dialog box

The textboxes display the content of the incoming data in hexadecimal and ASCII format,

respectively. To clear the Hexadecimal and ASCII textboxes, click Reset Scope.

Frame synchronization and Header data

As it is not possible to know when the ST7540 starts to demodulate data incoming from the

mains, a Frame Synchronization feature can be enabled in order to know when the data flow

begins.

If the Frame Synchronization feature is enabled (Frame Sync toggle switch), the data flow

from the ST7540 is filtered from the MCU and the data is sent to the PC only when a header

(defined by the Header parameter) is recognized. This ensures that all following bytes are

correctly sent to PC if the transmitted message is preceded by a preamble (i.e. 0xAAAA or

0x5555) and by a header (i.e. 0x9B58).

To mask the Header, enter the corresponding hexadecimal value in the Mask textbox. This

feature enables the use of less than 16 bits or more than one header. The Masked Header

textbox displays the masked header.

The Data Bytes parameter selects how many bytes the MCU must transmit to the PC after

a header recognition when in Frame Sync mode.

If frame synchronization is not required, the user can switch OFF the Frame Sync feature

and data are sent directly from the ST7540 to the PC. Note that since the first data

demodulation time is unpredictable, byte synchronization is not ensured.

Sensitivity modes

In addition to two sensitivity modes selectable through the Control Register Sensitivity Mode

(see Section 4.2.15: Sensitivity mode), it is possible to force ST7540 sensitivity to the BU

ST7540 RECEPTION WINDOW

RX Textboxes (Hex and ASCII)

Low Sensitivity

Frame synchronization controls

UM0239 Datasheet(PDF) 26 Page - STMicroelectronics