90E21 Datasheet, PDF (17/57 Pages) Integrated Device Technology – Single-Phase High-Performance Wide-Span Energy Metering IC

90E21/22/23/24
SINGLE-PHASE HIGH-PERFORMANCE WIDE-SPAN ENERGY METERING IC
4.1.2 THREE-WIRE MODE
In three-wire mode, CS is always at low level. When there is no oper-
ation, SCLK keeps at high level. The start of a read or write operation is
triggered if SCLK is consistently low for at least 400µs. The subsequent
read or write operation is similar to that in four-wire mode. Refer to Fig-
ure-8 and Figure-9.
CS
SCLK
SDI
SDO
CS
SCLK
SDI
SDO
Drive Low
Low ≥ 400µs
Don’t care
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Register address
A6 A5 A4 A3 A2 A1 A0
Don't care
Hign Impedance
16-bit data
DDDDDDDDDDDDDDDD
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Figure-8 Read Sequence in Three-Wire Mode
Low ≥ 400µs
1234
A6 A5 A4
High Impedance
Drive low
Low ≥ 400µs
Don't care
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Register Address
16-bit data
A6
A5
A4
A3
A2
A1
A0
D
15
D
14
D
13
D
12
D
11
D
10
D
9
D
8
D
7
D
6
D
5
D
4
D
3
D
2
D
1
D
0
High Impedance
Low ≥ 400µs
Don't care
1234
A6 A5 A4
Figure-9 Write Sequence in Three-Wire Mode
Interface
17
January 10, 2012