Fujitsu FR81S User Manual
CHAPTER 40: MULTI-FUNCTION SERIAL INTERFACE
5. Operation of UART
FUJITSU SEMICONDUCTOR LIMITED
CHAPTER : MULTI-FUNCTION SERIAL INTERFACE
FUJITSU SEMICONDUCTOR CONFIDENTIAL
141
5.1.2.
Reception Interrupts and Flag Setting Timing
Reception interrupts occur either when the reception is completed (SSR:RDRF) or when a reception error
occurs (SSR:PE, ORE, FRE).
When the first stop bit is detected, reception data is stored in the receive data register (RDR). When
reception is completed (SSR:RDRF=1) or a reception error occurs (SSR:PE, ORE, FRE=1), a
corresponding flag is set. If reception interrupts are enabled (SCR:RIE=1) at this time, a reception interrupt
occurs.
Note:
When a reception error occurs, the data in the receive data register (RDR) becomes invalid.
Figure 5-1 Timing of Flag Bit Setting
Timing to set RDRF(reception data full) flag bit
Reception data
RDRF
ST
D0
D1
D2
D5
D6
D7
SP
ST
Generation reception interrupt
Timing to set FRE(framing error) flag bit
Reception data
RDRF
(Notes)
•
A framing error occurs the first stop bit is at the “L” level.
•
RDRF is set to “1” and data is received even when a framing error occurs, but the reception data is
invalid.
ST
D0
D1
D2
D5
D6
D7
SP
ST
Generation of reception interrupt
FRE
Timing to set ORE(overrun error) flag bit
Reception data
RDRF
ORE
ORE
ST D0 D1 D2 D3 D4 D5 D6 D7 SP ST D0 D1 D2 D3 D4 D5 D6 D7 SP
(Note)
An overrun error occurs when the next data is transferred the reception data is read (RDRF=1).
MB91520 Series
MN705-00010-1v0-E
1454