Fujitsu FR81S User Manual
CHAPTER 40: MULTI-FUNCTION SERIAL INTERFACE
4. Registers
FUJITSU SEMICONDUCTOR LIMITED
CHAPTER : MULTI-FUNCTION SERIAL INTERFACE
FUJITSU SEMICONDUCTOR CONFIDENTIAL
122
Bit name
Function
bit2 RDRF:
Reception data full flag bit
"0" Read: Receive data register (RDR) is empty
"1" Read: Receive data register (RDR) contains data.
⋅
The flag indicates the state of the receive data register (RDR).
⋅
When the SMR:RIE bit and the reception data flag bit (RDRF) are "1", a
reception interrupt request will be output.
⋅
When received data is loaded in the RDR, this flag will be set to "1" and
when RDR is read out, it will be cleared to "0".
⋅
Set at the SCL falling timing in 8th bit of the data.
⋅
Also set at the NACK response *
1
.
⋅
While using reception FIFO, the RDRF will be set to "1" once the
reception FIFO has received the specified number of data sets.
⋅
While using reception FIFO, the bit will be cleared to "0" once the
reception FIFO becomes empty.
⋅
In the case where all the conditions below are met, when reception idle
continues for more than 8 baud rate clocks, interrupt flag (SSR:RDRF)
will be set to "1".
⋅
Reception FIFO idle detection enable bit (FCR:FRIIE) is "1"
⋅
Data count contained in the reception FIFO does not reach the transfer
count
⋅
IBCR:BER bit is "0"
If you read the RDR while the counter is counting 8 baud rate clocks, the
counter will be reset to 0 and start counting 8 clocks again.
*1: NACK response: indicates that SDA of I
2
C bus is "1" in the
acknowledge interval.
Note:
In the case were all of the conditions below are met, SCL is made "L" after
ACK is transmitted and SCL releases the state of "L" when the RDRF bit
becomes "0".
⋅
Reception FIFO is unused
⋅
DMA mode is enabled (IBCR:DMA="1")
⋅
RDRF bit is "1" while receiving second or latter byte data
(IBSR:TRX="0")
⋅
IBCR:WSEL="0"
In the case where all of the conditions below are met, SCL is made "L" after
1-byte data is received and SCL releases the state of "L" when the RDRF
bit becomes "0".
⋅
Reception FIFO is unused
⋅
DMA mode is enabled (IBCR:DMA="1")
⋅
RDRF bit is "1" while receiving second or latter byte data
(IBSR:TRX="0")
⋅
IBCR:WSEL="0"
In case of reception with the DMA mode enabled (DMA=1) and reception
FIFO used, SCL is made "L" when reception FIFO becomes full and SCL
releases the state of "L" when data is read out from RDR even once.
MB91520 Series
MN705-00010-1v0-E
1435