XR88C681_06 Datasheet, PDF (46/101 Pages) Exar Corporation – CMOS Dual Channel UART (DUART)

XR88C681
C.6.2.2 8086 Microprocessor
The 8086 microprocessor is a 16 bit microprocessor manufactured by Intel Corporation. Figure 20 presents the pin out
diagram of this IC. Please note that in Figure 20, pins 24 - 31 have some additional labels, located off to the right of the
package. These additional labels will be explained later in this text.
GND 1
AD14 2
AD13 3
AD12 4
AD11 5
AD10 6
AD9 7
AD8 8
AD7 9
AD6 10
AD5 11
AD4 12
AD3 13
AD2 ¹⁴
AD1 15
AD0 16
NMI 17
INTR 18
CLK 19
GND 20
8086 CPU
40 V_CC
39 AD15
38 _A16/S3
37 A17/S4
36 A18/S5
35 A19/S6
34 -BHE/S7
33 MN/MX
32 -RD
31 -RQ/-GT0
30 -RQ/-GT1
29 -LOCK
28 -S2
27 -S1
26 _-S0
25 QS0
24 _QS1
23 -TEST
22 READY
21 RESET
(HOLD)
(HLDA)
(-WR)
(M/-IO)
(DT/-R)
(-DEN)
(ALE)
(-INTA)
Figure 20. Pin Out of the 8086 Microprocessor Device
Intel went to great lengths to keep the pin count of this IC
low by multiplexing the functions of many of these pins.
This device consists of a 16 bit Data Bus and a 20 bit
Address Bus. The Data Bus is multiplexed with the lower
16 Address Bits (A0 - A15) to form AD0 - AD15. Address
Bits A16 - A19 are multiplexed with status bits S3 - S6 to
form A16/S3, A17/S4, A18/S5 and A19/S6. All of these
pins are address lines during the first half of a memory
cycle. However, during the second half of a memory
cycle, these pins then take on their alternate functions
Rev. 2.11
46