UPI-C42/UPI-L42
Table1. Pin Description (Continued)DIP PLCC QFP
Symbol Pin Pin Pin Type Nameand Function
No. No. No.
P20–P27 21–24 24–27 39–42 I/O PORT2: 8-bit, PORT 2 quasi-bidirectional I/O lines. The lower 4 bits
(P20–P23)interface directly to the 8243 I/O expander device and
35–38 39–42 11,13–15
containaddress and data information during PORT 4 –7 access. P21
canbe programmed to provide hardware A20 gate support. The upper
4bits (P24 –P27) can be programmed to provide interrupt Request and
DMAHandshake capability. Software control can configure P24 as
OutputBuffer Full (OBF) interrupt, P25 as Input Buffer Full (IBF)
interrupt,P26 as DMA Request (DRQ), and P27 as DMA ACKnowledge
(DACK).
PROG 25 28 43 I/O PROGRAM: Multifunction pin used as the program pulse input during
PROMprogramming.
DuringI/O expander access the PROG pin acts as an address/data
strobeto the 8243. This pin should be tied high if unused.
VCC 40 44 17 POWER: a5Vmain power supply pin.
VDD 26 29 1 POWER:a5V during normal operation. a12.75V during programming
operation.Low power standby supply pin.
VSS 20 22 38 GROUND:Circuit ground potential.
290414–4
Figure4. Block Diagram3