
XRT7245
DS3 UNI FOR ATM
á
PRELIMINARY
REV. 1.03
126
The circuitry in Figure 21 will function as follows during
a UNI requested interrupt. The UNI device would re-
quest an interrupt from the CPU by asserting its ac-
tive low INT* output pin. This will cause the INT0* in-
put pin of the CPU to go “l(fā)ow”. When this happens
the 8051 CPU will finish executing its current instruc-
tion, and will then branch program control the UNI in-
terrupt service routine. In the case of Figure 21, the
interrupt service routine will be located in 0003H in
code memory. The 8051 CPU does not issue an In-
terrupt Acknowledge signal back to the UNI. It will
just begin processing through the UNI’s interrupt ser-
vice routine. Once the CPU has eliminated the
cause(s) of the interrupt request, the UNI’s INT* pin
will be negated (go “high”) and the CPU will return
from the interrupt service routine and resume normal
operation.
3.8
Interfacing the UNI to a Motorola type
Microprocessor
This section discusses how to interface the XRT7245
DS3 UNI to the 68000 microprocessor.
Figure 22 presents a schematic on how to interface the
XRT7245 DS3 UNI to the MC68000 microprocessor,
over a 16 bit data bus.
F
IGURE
21. S
CHEMATIC
D
EPICTING
HOW
TO
I
NTERFACE
THE
XRT7245 DS3 UNI
TO
THE
8051 M
ICROCONTROLLER
5V
A[8:0]
D[15:8]
D[7:0]
AD[7:0]
A[15:9]
R
x
D
a
t
a
[
1
5
:
0
]
T
x
D
a
t
a
[
1
5
:
0
]
U3
74HC373
D0
D1
D2
D3
D4
D5
D6
D7
3
4
7
8
13
14
17
18
OC
G
1
11
Q0
Q1
Q2
Q3
Q4
Q5
Q6
Q7
2
5
6
9
12
15
16
19
U1
XR-T7245
TxNEG
111
TxPOS
109
TxLineClk
112
RxLineClk
99
RxNEG
98
RxPOS
97
D15
1
3
D14
4
D12
5
9
D11
11
D9
13
D8
14
D7
16
D6
17
D5
18
D4
19
D3
21
D2
23
D1
25
D0
28
A8
37
A7
40
A6
41
A5
42
A4
43
A3
44
A2
45
A1
46
A0
48
TxData15
144
142
TxData14
TxData12
140
TxData11
134
TTxData9
132
TxData8
130
TxData7
143
141
TxData6
TxData4
139
135
TxData3
133
TxData1
TxData0
131
MOTO/Intel
7
RxData0
RxData1
RxData2
RxData3
RxData5
RxData6
RxData7
RxData9
RxData10
RxData11
RxData13
RxData14
RxData15
70
68
64
62
60
58
56
54
69
67
65
63
61
57
55
53
Reset
RDS_DS
Rdy_Dtck
160
Width16
20
35
33
ALE_AS
34
Int
29
CS
32
U2
8051
WR
RD
16
17
AD0
AD1
AD2
AD4
AD5
AD7
39
38
37
36
35
34
33
32
ALE
30
A8
A9
A10
A12
A13
A14
21
22
23
24
25
26
27
28
INT0
INT1
12
13
To Address Decoder
From Address Decoder
RESET Command Circuitry
RxData[15:0]
TxData[15:0]