Uarti Baud Rate Register (Brgi) - Renesas 7700 FAMILY User Manual

7.2.6 UARTi baud rate register (BRGi)

The UARTi baud rate register (BRGi) is an 8-bit timer exclusively used for UARTi to generate a transfer
clock. It has a reload register. Assuming that a value set in the BRGi is "n" (n = "00
divides the count source frequency by n + 1.
In the clock synchronous serial I/O mode, the BRGi is valid when an internal clock is selected, and a clock
of which frequency is the BRGi output's frequency divided by 2 becomes the transfer clock. In the UART
mode, the BRGi is always valid, and a clock of which frequency is the BRGi output's frequency divided by
16 becomes the transfer clock.
The data which is written to the addresses 31
register whether transmission/reception is stopped or in progress. Accordingly, writing to their addresses,
perform it while that is stopped.
Figure 7.2.10 shows the structure of the UARTi baud rate register (BRGi); Figure 7.2.11 shows the block
diagram of transfer clock generating section.
b7
Fig. 7.2.10 Structure of UARTi baud rate register (BRGi)
<Clock synchronous serial I/O mode>
f BRGi
i
f
EXT
<UART mode>
f
i
f
EXT
f
i
f
EXT
Fig. 7.2.11 Block diagram of transfer clock generating section
b0
UART0 baud rate register (Address 31
UART1 baud rate register (Address 39
Bit
7 to 0 Can be set to "00
1/2
1/16
BRGi
1/16
: Clock selected by BRG count source select bits (f
: Clock input to CLK pin (external clock)
i
7751 Group User's Manual
and 39 is written to both the timer register and the reload
16 16
Functions
" to "FF
16 16
Assuming that the set value = n, BRGi
divides the count source frequency by n + 1.
Transmit control circuit
Receive control circuit
Transmit control circuit
Receive control circuit
/f , f
2 4
SERIAL I/O
7.2 Block description
" to "FF
16
)
16
)
16
At reset
."
Undefined
Transfer clock for transmit operation
Transfer clock for receive operation
Transfer clock for transmit operation
Transfer clock for receive operation
/f , f /f , or f /f )
16 32 64 128 512 1024
"), the BRGi
16
RW
WO
7–13