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8XC196MC, MD, MH USER’S MANUAL
7-12
7.4.3 Programming the Baud Rate and Clock Source
The SPx_BAUD register (Figure 7-7) selects the clock input for the baud-rate generator and de-
fines the baud rate for all serial I/O modes. (For mode 4 with SCLKx# configured for input, the
baud-rate generator is not used.) This register acts as a control register during write operations
and as a down-counter monitor during read operations.
WARNING
Writing to the SPx_BAUD register during a reception or transmission can
corrupt the received or transmitted data. Before writing to SPx_BAUD, check
the SPx_STATUS register to ensure that the reception or transmission is
complete.
SP
x
_BAUD
x
= 0–1 (8XC196MH)
Address:
Reset State:
1F84H, 1F8CH
0000H
The serial port baud rate
x
(SP
x
_BAUD) register selects the serial port
x
baud rate and clock source.
The most-significant bit selects the clock source. The lower 15 bits represent BAUD_VALUE, an
unsigned integer that determines the baud rate.
The maximum BAUD_VALUE is 32,767 (7FFFH). In asynchronous modes 1, 2, and 3, the minimum
BAUD_VALUE is 0000H when using XTAL1 and 0001H when using BCLK
x
. In synchronous mode 0,
the minimum BAUD_VALUE is 0001H for transmissions and 0002H for receptions. In synchronous
mode 4, the minimum BAUD_VALUE is 0001H for both transmissions and receptions.
15 8
8XC196MH CLKSRC
BV14 BV13 BV12 BV11 BV10 BV9 BV8
7 0
BV7 BV6 BV5 BV4 BV3 BV2 BV1 BV0
Bit
Number
Bit
Mnemonic
Function
15 CLKSRC Serial Port Clock Source
This bit determines whether the serial port is clocked from an internal or an
external source.
0 = signal on the BCLK
x
pin (external source)
1 = input frequency on the XTAL1 pin (internal source)
Figure 7-7. Serial Port
x
Baud Rate (SP
x
_BAUD) Register