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17-20 Intel® PXA26x Processor Family Developer’s Manual
Hardware UART
Note: Auto-baud rate detection is not supported with slow infrared Mode.
See Section 17.4.4, “Auto-Baud-Rate Detection”
for more information on auto-baud rate.
17.5.9 Auto-Baud Count Register (ACR)
The ACR stores the number of 14.7456-MHz-clock cycles within a start bit pulse. This value is
then used by the processor or the UART to calculate the baud rate. If auto-baud mode (ABR[ABE])
and auto-baud interrupts (ABR[ABLIE]) are enabled, the UART interrupts the processor with the
auto-baud lock interrupt (IIR[ABL]) after it has written the count value into the ACR. The value is
written regardless of the state of the auto-baud UART program bit (ABR[ABUP]).
The ACR bit
definitions are shown in
Table 17-13 on page 17-21.
Table 17-12. ABR Bit Definitions
Physical Address
0x4160_0028
Autobaud Control Reg. (ABR)
PXA26x processor family Hardware
UART
User
Settings
Bit 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Reserved
ABT
ABUP
ABLIE
ABE
Reset ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 0 0 0 0
Bits Access Name Description
31:4 N/A — Reserved – Read as unknown and must be written as zero.
3R/WABT
AUTOBAUD TABLE:
Uses a table to select low-speed baud rates instead of a formula. Only valid
if ABR[ABUP] is set.
0 – Table used to calculate baud rates which limits UART to choosing
common baud rates as shown in Section 17.4.4, “Auto-Baud-Rate
Detection”
1 – Formula used to calculate baud rates allowing all possible baud rates
to be chosen by UART.
2 R/W ABUP
AUTOBAUD UART PROGRAM:
Controls if the UART automatically programs DLL and DLH or if the
processor must program DLL and DLH based on the results in the ACR.
0 – Processor Programs Divisor Latch registers
1 – UART Programs Divisor Latch registers
1 R/W ABLIE
AUTOBAUD LOCK INTERRUPT ENABLE:
0 – Autobaud Lock Interrupt disabled (Source IIR[ABL])
1 – Autobaud Lock Interrupt enabled (Source IIR[ABL])
0R/WABE
AUTOBAUD ENABLE:
0 – Autobaud Disabled
1 – Autobaud Enabled