
AN155
Rev. 1.1 21
Figure D4. UART ISR
UART_ISR
receiver
interrupt flag
set?
receive buffer
full?
clear receiver flag.
read SBUF sfr.
put into readBuffer.
Increment readIndex.
Increment ReadCount.
transmitter
interrupt flag
set?
transmit buffer
empty?
clear transmitter flag.
get last char in WriteBuffer.
write to SBUF sfr.
decrement WriteCount.
drop character.
(dummy read)
Set TX_Idle flag
Return from
Interrupt.
Y
Y
Y
Y
N
N
N
N
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