Datasheet

ST7538Q Functional description
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5.11 Detection method and Rx Sensitivity in UART mode
When ST7538Q is running in UART mode (by forcing UART/SPI pin to “1”) the Control
Register Function “Detection method” differs from SPI mode as indicated in the Table 1 2:
UART mode provides also a third level of Receiving sensitivity in addition to two levels select
able by Control Register (see Ta bl e 11). By setting to “1” the TxD pin during a receiving
session the sensitivity is forced to BU threshold (this condition suppresses the Control
Register setting).
Table 12. Control register functions in UART mode
Function Value Selection Note Default
Bit 13 Bit 12
12 to
13
Detection
Method
Not Allowed 0 0
This configuration
should be avoided
because it could cause
an unpredictable
behavior of the device
Carrier
detection
without
conditioning
Not Allowed 0 1
This configuration
should be avoided
because it could cause
an unpredictable
behavior of the device
Carrier detection
without
conditioning
10
Carrier Detection
Notification on CD_PD
Line
CLR/T and RxD signal
always Present
Carrier detection
with conditioning
11
Carrier Detection
Notification on CD_PD
Line
CLR/T Line is forced to
“0” and RxD Line is
forced to “0” or “1”
(according the
UART/SPI pin level)
when Carrier is not
detected