Guard Time And Prescaler Register (Usart_Gtpr) - ST STM32F40 Series Reference Manual

RM0090
26.6.7

Guard time and prescaler register (USART_GTPR)

Address offset: 0x18
Reset value: 0x0000 0000
31 30 29
15 14 13
rw rw rw
Bits 31:16 Reserved, must be kept at reset value
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.
Universal synchronous asynchronous receiver transmitter (USART)
28 27 26 25
12 11 10 9
GT[7:0]
rw rw rw rw
2: This bit is not available for UART4 & UART5.
Doc ID 018909 Rev 4
24 23 22 21
Reserved
8 7 6 5
rw rw rw rw
20 19 18 17
4 3 2 1
PSC[7:0]
rw rw rw rw
16
0
rw
792/1422