
CHAPTER 15 ASYNCHRONOUS SERIAL INTERFACE (UART)
User
’
s Manual U15862EJ3V0UD
445
15.4 Control Registers
(1) Asynchronous serial interface mode register n (ASIMn)
The ASIMn register is an 8-bit register that controls the UARTn transfer operation.
This register can be read/written in 8-bit or 1-bit units.
Caution When using UARTn, be sure to set the external pins related to UARTn functions to the
control made before setting clock select register n (CKSRn) and the baud rate generator
control register n (BRGCn), and then set the UARTEn bit to 1. Then set the other bits.
(1/3)
<7>
UARTEn
ASIMn
<6>
TXEn
<5>
RXEn
4
PSn1
3
PSn0
2
CLn
1
SLn
0
ISRMn
After reset: 01H R/W Address: FFFFFA00H, FFFFFA10H, FFFFFA20H
UARTEn
Controls the operating clock
0
Stops clock supply to UARTn.
1
Supplies clock to UARTn.
If UARTEn = 0, UARTn is asynchronously reset.
If UARTEn = 0, UARTn is reset. To operate UARTn, first set UARTEn to 1.
If the UARTEn bit is changed from 1 to 0, all the registers of UARTn are initialized. To set UARTEn to 1 again, be
sure to re-set the registers of UARTn.
The output of the TXDn pin goes high when transmission is disabled, regardless of the setting of the UARTEn bit.
TXEn
Enables/disables transmission
0
Disables transmission
1
Enables transmission
Set the TXEn bit to 1 after setting the UARTEn bit to 1 at startup. Set the UARTEn bit to 0 after setting the TXEn
bit to 0 to stop.
To initialize the transmission unit, clear (0) the TXEn bit, and after letting 2 Clock cycles (base clock) elapse, set
(1) the TXEn bit again. If the TXEn bit is not set again, initialization may not be successful. (For details about the
base clock, refer to
15.7.1 (1) Base clock (Clock)
.)