Datasheet

113
AT89C5132
4173C–USB–07/04
Interrupt The Serial I/O Port handles two interrupt sources that are the “end of reception” (RI in
SCON) and “end of transmission” (TI in SCON) flags. As shown in Figure 90 these flags
are combined together to appear as a single interrupt source for the C51 core. Flags
must be cleared by software when executing the serial interrupt service routine.
The serial interrupt is enabled by setting ES bit in IEN0 register. This assumes interrupts
are globally enabled by setting EA bit in IEN0 register.
Depending on the selected mode and wether the framing error detection is enabled or
not, RI flag is set during the stop bit or during the ninth bit as detailed in Figure 91.
Figure 90. Serial I/O Interrupt System
Figure 91. Interrupt Waveforms
ES
IEN0.4
Serial I/O
Interrupt Request
TI
SCON.1
RI
SCON.0
RXD D0D1D2D3D4D5D6D7
Start Bit 8-bit Data Stop Bit
RI
S
MOD0 = X
FE
SMOD0 = 1
a. Mode 1
b. Mode 2 and 3
RXD D0D1D2D3D4D5D6 D8
Start bit 9-bit data Stop bit
RI
SMOD0 = 1
FE
SMOD0 = 1
D7
RI
SMOD0 = 0