CHAPTER 11 SERIAL INTERFACE FUNCTION
User’s Manual U15109EJ3V0UD
435
Figure 11-42. Block Diagram of UARTn
Baud rate generator
f
XX
to f
XX
/2
9
TXDn
ASCKn
RXDn
INTSTn
INTSRn
Internal bus
Selector
8
8
Receive shift register
n (RXn)
Receive buffer register
n (RXBn)
8
Transmit control
parity addition
Receive control
parity check
Transmit shift register
n (TXSn)
TMx output
Remarks
1.
n = 0 to 3
2.
TMx output is as shown below.
When n = 0, 2: TM6 output
When n = 1, 3: TM5 output
(1) Transmit shift registers 0 to 3 (TXS0 to TXS3)
TXSn is the register for setting transmit data. Data written to TXSn is transmitted as serial data.
When the data length is set as 7 bits, bit 0 to bit 6 of the data written to TXSn is transmitted as serial data.
Writing data to TXSn starts the transmit operation.
TXSn is written by an 8-bit memory manipulation instruction. It cannot be read.
RESET input sets these registers to FFH.
Caution
Do not write to TXSn during a transmit operation.
(2) Receive shift registers 0 to 3 (RX0 to RX3)
The RXn register converts serial data input via the RXDn pin to parallel data. When one byte of data is received
at RXn, the received data is transferred to receive buffer registers n (RXBn).
RXn cannot be manipulated directly by a program.
(3) Receive buffer registers 0 to 3 (RXB0 to RXB3)
RXBn is used to hold receive data. When one byte of data is received, one byte of new receive data is
transferred.
When the data length is set as 7 bits, received data is sent to bit 0 to bit 6 of RXBn. In RXBn, the MSB must be
set to 0.
RXBn is read by an 8-bit memory manipulation instruction. It cannot be written.
RESET input sets RXBn to FFH.