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Universal Asynchronous Receiver/Transmitters (UART) Modules
Factored Ratio: 184 ÷ 325
NUM = 183 (decimal) = 0x00B7
DENOM = 325 (decimal) = 0x0144
Baud Rate = (CKIH) ÷ (16 × Divisor)
or
Divisor = (CKIH) ÷ (16 × Baud Rate)
Transmitter Clock = 16 × Baud Rate
Receiver Clock = CKIH ÷ Divisor = 16 × Baud Rate
27.5.9 Baud Rate Automatic Detection Logic
When the baud rate automatic detection logic is enabled, the UART locks onto the incoming baud rate. To
enable this feature, set the automatic detection of baud rate bit (ADBR = 1) in the UART Control Register
1 and write 1 to the ADET bit in the UART Status Register 2 to clear it. When ADET=0 and ADBR =1, the
UART automatically sets the INC=0x0 (UBIR_1/UBIR_2) and MOD =0x0(UBMR_1/UBMR_2). it waits
for the start bit (transition from 1-to-0) and tries to lock onto the incoming baud rate. Once the start bit is
detected, the length of the start bit is calculated by counting until the 0-to-1 transition (see Figure 27-4 and
Section 27.5.9.1). The new baud rate is determined using this equation:
ADBR
Note:
same time this interrupt is set for the UART_MINT_UARTC signal.
Idle
Start
Bit
Note: LSB transmitted first.
The BRM INC (BIPR1_1/BIPR1_2 through BIPR4_1/BIPR4_2) and MOD (BMPR1_1/BMPR1_2
through BMPR4_1/BMPR4_2) preset registers are used when detecting the special baud rates (when
BPEN = 1). These registers are written by software before the start of automatic baud sequence detection.
After the auto baud count value is divided by 16 and a remainder higher than 3 is detected, the appropriate
27-16
BaudRate
Table 27-8. Baud Rate Automatic Detection
ADET
Baud Rate Detection
0
X
Manual Configuration
1
0
Auto Detection
1
1
Auto Detection
Complete
This table assumes that no other interrupt is set at the
1
0
0
Transition from 0-to-1
Figure 27-4. Baud Rate Detection Protocol Diagram
MC9328MX1 Reference Manual
Count
〈
〉
---------------- -
=
16
UART_MINT_UARTC
1
1
0
0
0
1
Eqn. 27-5
1
0
Stop
Bit
MOTOROLA
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