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© Andigilog, Inc. 2006
www.andigilog.com
October 2006 - 70A06010
aSC7621
Voltage Measurement and Limits
Register 20-24h: Voltage Reading
Register
Address
Read/
Write
Register Name
Bit 7
(MSB)
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
(LSB)
Default
Value
20h
R
2.5V (MS Byte)
9
8
7
6
5
4
3
2
N/A
13h
R
2.5V (LS Byte)
1
0
X
X
X
X
X
X
N/A
21h
R
VCCP (MS Byte)
9
8
7
6
5
4
3
2
N/A
18h
R
VCCP (LS Byte)
1
0
X
X
X
X
X
X
N/A
22h
R
3.3V (MS Byte)
9
8
7
6
5
4
3
2
N/A
11h
R
3.3V (LS Byte)
1
0
X
X
X
X
X
X
N/A
23h
R
5V (MS Byte)
9
8
7
6
5
4
3
2
N/A
12h
R
5V (LS Byte)
1
0
X
X
X
X
X
X
N/A
24h
R
12V (MS Byte)
9
8
7
6
5
4
3
2
N/A
14h
R
12V (LS Byte)
1
0
X
X
X
X
X
X
N/A
The Register Names define the typical input voltage at which the reading is ¾ full scale or C000h. High byte readings are 8-
bits with an LS bit value of Nominal divided by 192 and 2-bits in the high-order portion of the LS Byte having a value
corresponding to ½ and ¼ of that high byte LS bit value. Ignore the lower 6-bits of the LS Byte.
The Voltage Reading registers are updated automatically by the aSC7621 at a minimum frequency of 4Hz and a typical
frequency of 5 Hz. These registers are read only – a write to these registers has no effect.
Register 44-4Dh: Voltage Limit Registers
Register
Address
Read/
Write
Register Name
Bit 7
(MSB)
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
(LSB)
Default
Value
44h
R/W
2.5V Low Limit
7
6
5
4
3
2
1
0
00h
45h
R/W
2.5V High Limit
7
6
5
4
3
2
1
0
FFh
46h
R/W
VCCP Low Limit
7
6
5
4
3
2
1
0
00h
47h
R/W
VCCP High Limit
7
6
5
4
3
2
1
0
FFh
48h
R/W
3.3V Low Limit
7
6
5
4
3
2
1
0
00h
49h
R/W
3.3V High Limit
7
6
5
4
3
2
1
0
FFh
4Ah
R/W
5V Low Limit
7
6
5
4
3
2
1
0
00h
4Bh
R/W
5V High Limit
7
6
5
4
3
2
1
0
FFh
4Ch
R/W
12V Low Limit
7
6
5
4
3
2
1
0
00h
4Dh
R/W
12V High Limit
7
6
5
4
3
2
1
0
FFh
If a voltage input either exceeds the value set in the voltage high limit register or falls below the value set in the voltage low
limit register, the corresponding bit will be set automatically by the aSC7621 in the interrupt status registers (41-42h). The
binary value of the voltage limits are extended to 16-bits and compared with the two-bytes of the voltage reading. Voltages
are presented in the registers at ¾ of full-scale for the nominal voltage, meaning that at nominal voltage, each input will be
C0h, as shown in Table 11. Note that 3.3V input is Vdd and is not allowed to go below 3.0V during normal operation.
Setting the Ready/Lock/Start/Override register Lock bit has no effect on these registers.
Input
Nominal
Voltage
Register Reading
at Nominal
Voltage
Maximum
Voltage
Register Reading
at Maximum
Voltage
Minimum
Voltage
Register Reading
at Minimum
Voltage
2.5V
2.5V
C0h
3.32V
FFh
0V
00h
VCCP
2.25V
C0h
3.00V
FFh
0V
00h
3.3V
3.3V
C0h
4.38V
FFh
3.0V
AEh
5V
5.0V
C0h
6.64V
FFh
0V
00h
12V
12.0V
C0h
16.00V
FFh
0V
00h
Table 11 Voltage Limits vs Register Setting (MS Byte)
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