Intel 8253 - Page 122

Philips Semiconductors Product specification
80C31/80C32
80C51 8-bit microcontroller family
128/256 byte RAM ROMless low voltage (2.7V–5.5V),
low power, high speed (33 MHz)
2000 Aug 07
16
SMOD1 SMOD0 – POF GF1 GF0 PD IDL
PCON
(87H)
SM0 / FE SM1 SM2 REN TB8 RB8 TI RI
SCON
(98H)
D0 D1 D2 D3 D4 D5 D6 D7 D8
STOP
BIT
DATA BYTE
ONLY IN
MODE 2, 3
START
BIT
SET FE BIT IF STOP BIT IS 0 (FRAMING ERROR)
SM0 TO UART MODE CONTROL
0 : SCON.7 = SM0
1 : SCON.7 = FE
SU01191
Figure 8. UART Framing Error Detection
SM0 SM1 SM2 REN TB8 RB8 TI RI
SCON
(98H)
D0 D1 D2 D3 D4 D5 D6 D7 D8
1
1
1
0
COMPARATOR
11 X
RECEIVED ADDRESS D0 TO D7
PROGRAMMED ADDRESS
IN UART MODE 2 OR MODE 3 AND SM2 = 1:
INTERRUPT IF REN=1, RB8=1 AND “RECEIVED ADDRESS” = “PROGRAMMED ADDRESS”
– WHEN OWN ADDRESS RECEIVED, CLEAR SM2 TO RECEIVE DATA BYTES
– WHEN ALL DATA BYTES HAVE BEEN RECEIVED: SET SM2 TO WAIT FOR NEXT ADDRESS.
SU00045
Figure 9. UART Multiprocessor Communication, Automatic Address Recognition