Determining Serial Port Status - Intel 8XC196MC User Manual

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7.4.5

Determining Serial Port Status

You can read the SPx_STATUS register (Figure 7-8) to determine the status of the serial port.
Reading SPx_STATUS clears all bits except TXE. For this reason, we recommend that you copy
the contents of the SPx_STATUS register into a shadow register and then execute bit-test instruc-
tions such as JBC and JBS on the shadow register. Otherwise, executing a bit-test instruction
clears the flags, so any subsequent bit-test instructions will return false values. You can also read
the interrupt pending register or peripheral interrupt pending register (see Table 7-2 on page 7-2)
to determine the status of the serial port interrupts.
SP x _STATUS
x = 0–1 (8XC196MH)
The serial port status (SP x _STATUS) register contains bits that indicate the status of serial port x .
7
8XC196MH
RPE/RB8
Bit
Bit
Number
Mnemonic
7
RPE/RB8
6
RI
5
TI
4
FE
3
TXE
2
OE
1:0
Figure 7-8. Serial Port Status (SP x _STATUS) Register
RI
TI
FE
Received Parity Error/Received Bit 8
RPE is set if parity is disabled (SP x _CON.2 = 0) and the ninth data bit
received is high.
RB8 is set if parity is enabled (SP x _CON.2 = 1) and a parity error occurred.
Reading SP x _STATUS clears this bit.
Receive Interrupt
This bit is set when the last data bit is sampled. Reading SP x _STATUS
clears this bit.
Transmit Interrupt
This bit is set at the beginning of the stop bit transmission. Reading
SP x _STATUS clears this bit.
Framing Error
This bit is set if a stop bit is not found within the appropriate period of time.
Reading SP x _STATUS clears this bit.
SBUF x _TX Empty
This bit is set if the transmit buffer is empty and ready to accept up to two
bytes. It is cleared when a byte is written to SBUF x _TX.
Overrun Error
This bit is set if data in the receive shift register is loaded into SBUF x _RX
before the previous bit is read. Reading SP x _STATUS clears this bit.
Reserved; for compatibility with future devices, write zeros to these bits.
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SERIAL I/O (SIO) PORT
Address:
Reset State:
TXE
OE
Function
1F81H, 1F89H
00H
0
7-15

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