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Universal synchronous asynchronous receiver transmitter (USART) RM0008

648/690

24.6.7 Guard time and prescaler register (USART_GTPR)

Address offset: 0x18

Reset value: 0x0000

31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16

Reserved

1514131211109876543210

GT[7:0] PSC[7:0]

rw rw rw rw rw rw rw rw rw rw rw rw rw rw rw rw

Bits 31:16 Reserved, forced by hardware to 0.

Bits 15:8 GT[7:0]: Guard time value.

This bit-field gives the Guard time value in terms of number of baud clocks.

This is used in Smartcard mode. The Transmission Complete flag is set after this guard time value.

Note: This bit is not available for UART4 & UART5.

Bits 7:0 PSC[7:0]: Prescaler value.

– In IrDA Low-power mode:

PSC[7:0] = IrDA Low-Power Baud Rate

Used for programming the prescaler for dividing the system clock to achieve the low-power

frequency:

The source clock is divided by the value given in the register (8 significant bits):

00000000: Reserved - do not program this value

00000001: divides the source clock by 1

00000010: divides the source clock by 2

...

– In normal IrDA mode: PSC must be set to 00000001.

– In smartcard mode:

PSC[4:0]: Prescaler value.

Used for programming the prescaler for dividing the system clock to provide the smartcard clock.

The value given in the register (5 significant bits) is multiplied by 2 to give the division factor of the

source clock frequency:

00000: Reserved - do not program this value

00001: divides the source clock by 2

00010: divides the source clock by 4

00011: divides the source clock by 6

...

Note 1: Bits [7:5] have no effect if Smartcard mode is used.

Note 2: This bit is not available for UART4 & UART5.

ST STM32F102 series User Manual

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