UPD780078 Datasheet, PDF (290/592 Pages) NEC – 8-Bit Single-Chip Microcontrollers

CHAPTER 15 SERIAL INTERFACE UART2
Caution
Do not rewrite asynchronous serial interface mode register 2 (ASIM2) during a transmit
operation. Rewriting the ASIM2 register during a transmit operation may disable further
transmit operations (in such cases, input a RESET to restore normal operation).
(d) Successive transmission
The next transmit data can be written to transmit buffer register 2 (TXB2) as soon as transmit shift register
2 (TXB2) has started its shift operation. Consequently, even while an interrupt is being serviced after one
data frame has been transmitted, data can be successively transmitted.
To successively transmit data, be sure to check, by using asynchronous serial interface transmit status
register 2 (ASIF2), the transmission status and whether writing to TXB2 is enabled or disabled, and then
write the data to TXB2.
The following table shows the relationship between the transmission status and writing to TXB2.
Table 15-5. Writing to TXBF and TXB2 (When Successive Transmission Is Started)
TXBF
0
1
Enabled
Disabled
Writing to TXB2 When Successive Transmission Is Started
Caution When starting successive transmission, write the first byte of data to transmit buffer
register 2 (TXB2), and then make sure to write data to TXB2 again.
Remark TXBF: Bit 1 of ASIF2
Table 15-6. Writing to TXSF and TXB2 (When Successive Transmission Is in Progress)
TXSF
0
1
Writing to TXB2 When Successive Transmission Is in Progress
Two-byte writing or transmit completion processing enabled
One-byte writing enabled
Cautions 1. When successive transmission is in progress, the processing of writing to TXB2 can
be confirmed by checking the value of TXSF after the transmit completion interrupt.
• TXSF = 1: Successive transmission in progress. One-byte data can be written.
• TXSF = 0: Successive transmission is complete. Two-byte data can be written.
When writing, note the Caution in Table 15-5.
2. To initialize (to set TXE2 to 0 or POWER2 to 0) during successive transmission, make
sure that TXSF is 0 after the transmit completion interrupt, then initialize.
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User’s Manual U14260EJ3V1UD