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7641

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

Mitsumi 

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MITSUBISHI MICROCOMPUTERS

7641 Group

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

UART Transmit Operation

Transmission starts when the Transmit Enable Bit is “1” and the

Transmit Buffer Empty Flag is “0”. Additionally, when CTS function

enabled, the CTSx pin must be “L” to be started. The data in which

Start Bit and Stop Bit or Parity Bit are also added is transmitted

from the low-order byte sequentially. When using 9-bit character

length, set the data into the UARTx transmit buffer register 2

(high-order byte) first before the UARTx transmit buffer register 1

(low-order byte).

Once the transmission starts, the Transmit Enable Bit, the Trans-

mit Buffer Empty Flag and the CTSx pin state (when this is

enabled) could not be checked until the transmission in progress

has ended.

Transmission requires the following setup:

(1) Define a baud rate by setting a value n (n = 0 to 255) into

UARTx baud rate generator (addresses 003116, 003916).

(2) Set the Transmit Initialization Bit (bit 2 of UxCON) to “1”. This

will set the UARTx status register to “0316”.

(3) Select the interrupt source with the Transmit Interrupt Source

Select Bit (bit 4 of UxCON).

(4) Configure the data format and clock selection by setting the

UARTx mode register.

(5) Set the CTS Function Enable Bit (bit 5 of UxCON) if CTS func-

tion will be used.

(6) Set the Transmit Enable Bit (bit 0 of UxCON) to “1”.

If updating a value of UARTx baud rate generator while the data is

being transmitted, be sure to disable the transmission before up-

dating. If the former data remains in the UARTx transmit buffer

registers 1 and 2 at retransmission, an undefined data might be

output.

UART Receive Operation

Reception is enabled when the Receive Enable Bit is “1”. Detec-

tion of the start bit makes transfer clocks generated and the data

reception starts in the LSB first.

When using 9-bit character length, read the received data from the

UARTx receive buffer register 2 (high-order byte) first before the

UARTx receive buffer register 1 (low-order byte).

Reception requires the following setup:

(1) Define a baud rate by setting a value n (n = 0 to 255) into

UARTx baud rate generator (addresses 003116, 003916).

(2) Set the Receive Initialization Bit (bit 3 of UxCON) to “1”.

(3) Configure the data format and clock selection by setting the

UARTx mode register.

(4) Set the RTS Function Enable Bit (bit 5 of UxCON) if RTS func-

tion will be used.

(5) Set the Receive Enable Bit (bit 1 of UxCON) to “1”.

CTS (Clear-to-Send) Function

As a transmitter, the UART can be configured to recognize the

Clear-to-Send (CTSx) input as a handshaking signal. This is en-

abled by setting the CTS Function Enable Bit (bit 5 of UxCON) to

“1”. If CTS function is enabled, even when transmission is enabled

and the UARTx transmit buffer register is filled with the data, the

transmission never starts; but it will start when inputting “L” to the

CTSx pin.

Figures 27 and 28 show the UARTx transmit timings.

Transfer clock

Tranmit enable bit

Transmit buffer

empty flag

CTSx pin

(P86/CTS1, P82/CTS2/SRXD)

UTXD output (P84/UTXD1,

P80/UTXD2/SRDY)

Transmit complete flag

Data set into UARTx transmit buffer register 1

Data transferring from UARTx

transmit buffer register 1 to Transmit shift register 1

Halt due to CTS = “H”

Halt due to Tranmit

enable bit = “0”

ST D0 D1 D2 D3 D4 D5 D6 D7 P SP

ST D0 D1 D2 D3 D4 D5 D6 D7 P SP

This timing applying to the conditions:

•Character length = 8 bits

•Parity enabled

•1 stop bit

Fig. 27 UARTx transmit timing (CTS function enabled)

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