CHAPTER 10 SERIAL INTERFACE FUNCTION
User’s Manual U13850EJ4V0UM
313
Figure 10-32. Block Diagram of UARTn
Baud rate generator
f
XX
to f
XX
/2
9
TXD0, TXD1
ASCK0, ASCK1
RXD0, RXD1
INTST0,
INTST1
INTSR0,
INTSR1
0, 1 (RX0, RX1)
Internal bus
Selector
0, 1 (TXS0, TXS1)
8
8
Receive shift registers
Receive buffer registers
0, 1 (RXB0, RXB1)
8
Transmit control
parity addition
Receive control
parity check
Transmit shift registers
TMx output
Remark
TMx output is as follows:
When UART0: TM2
When UART1: TM3
(1) Transmit shift registers 0, 1 (TXS0, TXS1)
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 can be written to by an 8-bit memory manipulation instruction. It cannot be read from.
RESET input sets these registers to FFH.
Caution
Do not write to TXSn during a transmit operation.
(2) Receive shift registers 0, 1 (RX0, RX1)
RXn register converts serial data input via the RXD0, RXD1 pins to parallel data. When one byte of data is
received at RXn, the received data is transferred to receive buffer registers 0, 1(RXB0, RXB1).
RX0, RX1 cannot be manipulated directly by a program.
(3) Receive buffer registers 0, 1 (RXB0, RXB1)
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 can be read by an 8-bit memory manipulation instruction. It cannot be written to.
RESET input sets RXBn to FFH.