NEC PD703114, Руководство пользователя

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CHAPTER 10 SERIAL INTERFACE FUNCTION
User’s Manual U15195EJ5V0UD
469
(c) Prescaler compare register 1 (PRSCM1)
PRSCM1 is an 8-bit compare register that sets the value of the 8-bit timer counter.
This register can be read/written in 8-bit units.
Cautions 1. The internal timer counter is cleared by writing to the PRSCM1 register. Therefore,
do not overwrite the PRSCM1 register during a transmission operation.
2. Perform PRSCM1 register settings prior to setting the UARTCE1 bit to 1. If the
contents of the PRSCM1 register are overwritten when the value of the UARTCE1
bit is 1, the cycle of the baud rate signal is not guaranteed.
3. Set the baud rate in the asynchronous mode to 153600 bps or lower. Set the baud
rate in the synchronous mode to 1000000 bps or lower.
7
PRSCM7 PRSCM1
6
PRSCM6
5
PRSCM5
4
PRSCM4
3
PRSCM3
2
PRSCM2
1
PRSCM1
0
PRSCM0
Address
FFFFFA30H
After reset
00H
(d) Baud rate generation
First, when the UARTCE1 bit of the PRSM1 register is overwritten by 1, the 8-bit timer counter for baud
rate signal generation starts counting up with the clock selected by bits BGCS1 and BGCS0 of the
PRSM1 register. The count value of the 8-bit timer counter is compared with the value of the PRSCM1
register, and if these values match, a timer count clock pulse of 1 cycle is output to the output controller
for the baud rate.
The output controller for the baud rate reverses the baud rate signal in synchronization with the rising
edge of the timer count clock when this pulse is “1”.
(e) Cycle of baud rate signal
The cycle of the baud rate signal is calculated as follows.
•
When setting value of PRSCM1 register is 00H
(Cycle of signal selected by bits BGCS1, BGCS0 of PRSM1 register)
×
256
×
2
•
In cases other than above
(Cycle of signal selected by bits BGCS1, BGCS0 of PRSM1 register)
×
(setting value of PRSCM1
register)
×
2