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11-134 SA-1100
Developer’s Manual
Peripheral Control Module
11.11.4 UART Control Registers 1 and 2
UART control register 1 (UTCR1) contains the upper 4 bits and UTCR2 the lower 8 bits of the
baud rate divisor field.
11.11.4.1 Baud Rate Divisor (BRD)
The 12-bit baud rate divisor (BRD) field is used to select the baud or bit rate of the UART. A total
of 4096 different baud rates can be selected, ranging from a minimum of 56.24 bps to a maximum
of 230.4 Kb/ps. The baud rate generator uses the 3.6864-MHz clock generated by the on-chip PLL
divided by 16 to generate the bit clock. A digital PLL is used to synchronize the baud rate of the
receiver each time the start bit is detected on the receive pin and each bit of the receive data stream
is sampled on the eighth clock of the divide by 16 counter (halfway through the bit period). The
resultant baud rate, given a specific BRD value or required BRD value and given a desired baud
rate, can be calculated using the following two respective equations, where BRD is the decimal
equivalent of the binary value programmed within the bit field:
The following tables show the bit locations corresponding to the baud rate divisor field that is split
between two 8-bit registers. The upper four bits of BRD reside within UTCR1 and the lower eight bits
reside within UTCR2. The UART must be disabled (RXE=TXE=0) whenever these registers are written.
The reset state of the BRD field is unknown (indicated by question marks) and must be initialized before
enabling the UART. Note that writes to reserved bits are ignored and reads return zeros.
BaudRate
3.6864
6
×10
16
x
BRD
1+
()
---------------------------------------=
BRD
3.6864
6
×10
16x
BaudRate
----------------------------------------1–=
Address: 0h 8005 0004 UTCR1 Read/Write
Bit 76543210
Reserved BRD<11:8>
Reset0000????
Bit Name Description
3..0 BRD<11:8>
Baud rate divisor.
Encoded value (from 0 to 4096) used to generate the baud rate of the UART.
Baud Rate = 3.6864x10
6
/(16x(BRD+1)), where BRD is a decimal value.
7..4 — Reserved.
Address: 0h 8005 0008 UTCR2 Read/Write
Bit 76543210
BRD<7:0>
Reset????????
Bit Name Description
7..0 BRD<7:0>
Baud rate divisor.
Encoded value (from 0 to 4096) used to generate the baud rate of the UART.
Baud Rate = 3.6864x10
6
/(16x(BRD+1)), where BRD is a decimal value.