
á
FOUR CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
XRT72L54
PRELIMINARY
REV. P1.1.2
138
does not issue an Interrupt Acknowledge signal back
to the Framer IC. It will just begin processing through
the Framer’s interrupt service routine. One the CPU
has eliminated the cause(s) of the interrupt request,
the Framer’s INT output pin will be negated (e.g., go
"High”) and the CPU will return from the Interrupt Ser-
vice Routine and resume normal operation.
2.9
INTERFACING THE FRAMER IC TO A MOTOROLA-
TYPE
MICROPROCESSOR
This section discusses how to interface the
XRT72L54 DS3/E3 Framer IC to the MC68000 Micro-
processor.
Figure 38 presents a schematic on how to interface
the XRT72L54 DS3/E3 Framer IC to the MC68000
Microprocessor, over an 8-bit wide bi-directional data
bus.
In general, the approach to interfacing these two de-
vices is straightforward. However, the user must be
aware of the fact that the XRT72L54 DS3/E3 Framer
IC does not provide an interrupt vector to the
MC68000 during an Interrupt Acknowledge cycle.
Therefore, the user must configure his/her design to
support auto-vectored interrupts. Auto-vectored in-
terrupt processing is a feature offered by the
MC68000 Family of Microprocessors, where, if the
microprocessor knows (prior to any IACK cycle) the
Interrupt Level of this current interrupt, and that the
interrupting peripheral does not support vectored in-
terrupts, then the Microprocessor will generate its
own Interrupt Vector. The schematic shown in
Figure 38, has been configured to support auto-vec-
tored interrupts.
Functional Description of Circuit illustrated in
When the XRT72L54 DS3/E3 Framer IC generates
an Interrupt, the INT output will toggle "Low”. This will
force Input 6, of the Interrupt Priority Encoder chip
(U4) to also toggle "Low”. In response to this, the In-
FIGURE 38. SCHEMATIC DEPICTING HOW TO INTERFACE THE XRT72L54 DS3/E3 FRAMER IC TO THE MC68000
MICROPROCESSOR
1
U9B
74HC04
3
4
1
U9A
74HC04
1
2
To Address Decoder
BIN/OCT
0
1
2
3
4
5
6
7
1
2
4
&EN
U11
74ACT138
6
4
5
1
2
3
15
14
13
12
11
10
9
7
&
U8A
74HCT00
1
2
3
D[15:8]
3.3V
5V
DATA_STROBE*
ADDRESS_STROBE*
1
2
4E N
HPRI/BIN
1
-
0/Z10
1/Z11
2/Z12
3/Z13
4/Z14
5/Z15
6/Z16
7/Z17
V18
10
11
12
13
14
15
16
17
18
U10
74HC148
5
4
3
2
1
13
12
11
10
6
7
9
14
15
DATA_STROBE*
U7
XRT72L54
T19
P17
J17
L18
L20
K20
K19
K18
K17
J20
J19
R20
P18
P19
P20
N18
N19
N20
M17
M18
H20
R18
T20
V20
R19
M19
M20
RESET
WR_RW
Rdy_Dtck
D0
D1
D2
D3
D4
D5
D6
D7
A0
A1
A2
A3
A4
A5
A6
A7
A8
INT
CS
MOTO/INTEL
RD_DS
ALE_AS
A9
A10
XRT72L54_CS*
BIN/OCT
0
1
2
3
4
5
6
7
1
2
4
&EN
U12
74ACT138
6
4
5
1
2
3
15
14
13
12
11
10
9
7
U6
MC68000
18
9
10
5
4
3
2
1
64
63
62
61
60
59
58
57
56
55
54
29
30
31
32
33
34
35
36
37
28
27
26
21
25
24
23
6
7
8
38
39
40
41
42
43
44
45
46
47
48
49
50
51
RESET
R/W
DTACK
D0
D1
D2
D3
D4
D5
D6
D7
D8
D9
D10
D11
D12
D13
D14
D15
A1
A2
A3
A4
A5
A6
A7
A8
A9
FC0
FC1
FC2
VPA
IPL0
IPL1
IPL2
AS
UDS
LDS
A10
A11
A12
A13
A14
A15
A16
A17
A18
A19
A20
A21
A22
A23