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VID Code Monitoring
The ADT7476A has five dedicated voltage ID (VID code)
inputs. These are digital inputs that can be read back through
the VID/GPIO register (0x43) to determine the processor
voltage required or the system being used. Five VID code
inputs support VRM9.x solutions. In addition, Pin 21 (12 V
input) can be reconfigured as a sixth VID input to satisfy
future VRM requirements.
VID/GPIO Register (0x43)
[0] = VID0, reflects logic state of Pin 5.
[1] = VID1, reflects logic state of Pin 6.
[2] = VID2, reflects logic state of Pin 7.
[3] = VID3, reflects logic state of Pin 8.
[4] = VID4, reflects logic state of Pin 19.
[5] = VID5, reconfigurable 12 V input. This bit reads 0 when
Pin 21 is configured as the 12 V input. This bit reflects the
logic state of Pin 21 when the pin is configured as VID5.
VID Code Input Threshold Voltage
The switching threshold for the VID code inputs is
approximately 1.0 V. To enable future compatibility, it is
possible to reduce the VID code input threshold to 0.6 V.
Bit 6 (THLD) of the VID/GPIO register (0x43) controls the
VID input threshold voltage.
VID/GPIO Register (0x43)
[6] THLD = 0, VID switching threshold = 1 V,
V
< 0.8 V, V
OL
[6] THLD = 1, VID switching threshold = 0.6 V,
V
< 0.4 V, V
OL
Reconfiguring Pin 21 as VID5 Input
Pin 21 can be reconfigured as a sixth VID code input
(VID5) for VRM10 compatible systems. Because the pin is
configured as VID5, it is not possible to monitor a 12 V
supply.
Bit 7 of the VID/GPIO register (0x43) determines the
function of Pin 21. System or BIOS software can read the
state of Bit 7 to determine whether the system is designed to
monitor 12 V or a sixth VID input.
VID/GPIO Register (0x43)
[7] VIDSEL = 0, Pin 21 functions as a 12 V measurement
input. Software can read this bit to determine that there are
five VID inputs being monitored. Bit 5 of VID/GPIO
Register (0x43) always reads back 0. Bit 0 of Interrupt
Status Register 2 (0x42) reflects 12 V out-of-limit
measurements.
[7] VIDSEL = 1, Pin 21 functions as the sixth VID code
input (VID5). Software can read this bit to determine that
there are six VID inputs being monitored. Bit 5 of
Register 0x43 reflects the logic state of Pin 21. Bit 0 of
Interrupt Status Register 2 (0x42) reflects VID code
changes.
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> 1.7 V, V
= 3.3 V.
IH
MAX
> 0.8 V, V
= 3.3 V.
IH
MAX
ADT7476A
VID Code Change Detect Function
The ADT7476A has a VID code change detect function.
When Pin 21 is configured as the VID5 input, VID code
changes are detected and reported back by the ADT7476A.
Bit 0 of Interrupt Status Register 2 (0x42) is the 12 V/VC bit
and denotes a VID change when set. The VID code change
bit is set when the logic states on the VID inputs are different
than they were 11 ms previously. The change of VID code is
used to generate an SMBALERT interrupt. If an
SMBALERT interrupt is not required, Bit 0 of Interrupt
Mask Register 2 (0x75), when set, prevents SMBALERTs
from occurring on VID code changes.
Interrupt Status Register 2 (0x42)
[0] 12 V/VC = 0, if Pin 21 is configured as VID5, Logic 0
denotes no change in VID code within the last 11 ms.
[0] 12 V/VC = 1, if Pin 21 is configured as VID5, Logic 1
means that a change has occurred on the VID code inputs
within the last 11 ms. An SMBALERT is generated, if this
function is enabled.
Programming the GPIOs
The ADT7476A follows an upgrade path from the
ADM1027 to the ADT7476A. In order to maintain
consistency between versions, it is necessary to omit
references to GPIO5. As a result, there are six GPIOs as
follows: GPIO0, GPIO1, GPIO2, GPIO3, GPIO4, and
GPIO6.
Setting Bit 4 of Configuration Register 5 (0x7C) to 1
enables GPIO functionality. This turns all pins configured as
VID inputs into general-purpose outputs. Writing to the
corresponding VID bit in the VID/GPIO register (0x43) sets
the polarity for the corresponding GPIO. GPIO6 can be
programmed independently as, for example, an input or
output, using Bits [3:2] of Configuration Register 5 (0x7C).
Temperature Measurement Method
Local Temperature Measurement
The ADT7476A contains an on-chip band gap
temperature sensor whose output is digitized by the on-chip,
10-bit ADC. The 8-bit MSB temperature data is stored in the
temperature registers (Addresses 0x25, 0x26, and 0x27).
Because both positive and negative temperatures can be
measured, the temperature data is stored in Offset 64 format
or twos complement format, as shown in Table 14 and
Table 15. Theoretically, the temperature sensor and ADC
can measure temperatures from −63°C to +127°C (or −61°C
to +191°C in the extended temperature range) with a
resolution of 0.25°C. However, this exceeds the operating
temperature range of the device, so local temperature
measurements
temperature range are not possible.
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16
outside
the
ADT7476A
operating
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