11
FIGURE 11. MODE CONTROL WORD FIGURE 12. MODE 2NOTE: Any sequence whereWR occurs before ACK andSTB occurs before RD is permissible. (INTR = IBF • MASK•STB •RD ÷OBF •MASK•ACK •WR)FIGURE 13. MODE 2 (BI-DIRECTIONAL)1
D7 D6 D5 D4 D3 D2 D1 D0
CONTROL WORD
1/0 1/01 1/0
PC2-PC0
1 = INPUT
0 = OUTPUT
PORT B
1 = INPUT
0 = OUTPUT
GROUP B MODE
0 = MODE 0
1 = MODE 1
PC7 OBFA
PC6
INTE
PA7-PA0
ACKA
IBFA
PC4
WR
INTE
RD
PC3
PC5
PC2-PC0
1
2
8
STBA
3I/O
INTRA
tWOB
tAOB
tAK
tAD tKD
tPH
tPS
tSIB
tST
OBF
WR
INTR
ACK
IBF
STB
PERIPHERAL
BUS
RD
tRIB
DATA FROM
PERIPHERAL TO 82C55A DATA FROM
82C55A TO PERIPHERAL
DATA FROM
82C55A TO CPU
DATA FROM
CPU TO 82C55A
82C55A