UM0239 datasheet(19/44 Pages) STMICROELECTRONICS

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UM0239

Getting started

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4.2.12

Frame length count

Frame Length Count parameter (Bit 19) is related to the Header Recognition function.

If enabled, receiving data are put on RxD line and CLR/T becomes active only after a

header recognition and only for the number of (16-bit) data words indicated by the Frame

Length parameter (Bits [47:40]).

Header Recognition is signaled to the host through the CD/PD line that is held low during

RxD and CLR/T activation.

If the Frame Length Count parameter is disabled, the header recognition is signaled by

forcing down the CD/PD line for one CLR/T line period while lines RxD and CLR/T are

always active.

This function is available only if the Extended Control Register parameter (Bit 21) is

enabled.

4.2.13

Header length

The Header Length parameter (Bit 20) is related to Header Recognition function and defines

the length of the header to recognize (8 or 16 bits).

If an 8-bit header is selected, two headers can be used since the Frame Header parameter

(Bits [39:24]) consists of 16 bits.

This function is available only if the Extended Control Register parameter (Bit 21) is

enabled.

4.2.14

Extended control register

The Extended Control Register parameter (Bit 21) enables the extended functions: Output

Voltage Freeze and Header Recognition. If enabled, 24 or 48 bits can be transmitted to the

ST7540 (the software always transmits 48 bits when enabled).

Table 14.

Header recognition

Bit 17

Value

Disabled (default)

1Enabled

Table 15.

Frame Length Count

Bit 19

Value

Disabled (default)

1Enabled

Table 16.

Header Length

Bit 20

Value

08 bits

16 bits (default)

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