adt7476a Analog Devices, Inc., adt7476a Datasheet - Page 18

• Manufacturer Part Number: adt7476a
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

ADT7476A
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 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
[6] THLD = 1, VID switching threshold = 0.6 V,
V
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
OL
OL
< 0.8 V, V
< 0.4 V, V
IH
IH
> 1.7 V, V
> 0.8 V, V
MAX
MAX
= 3.3 V.
= 3.3 V.
Rev. 0 | Page 18 of 72
the logic state of Pin 21. Bit 0 of Interrupt Status Register 2
(0x42) reflects VID code changes.
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 μs
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 SMBALERT s from occurring on VID code changes.
Interrupt Status Register 2 (0x42)
[0] 12V/VC = 0, if Pin 21 is configured as VID5, Logic 0
denotes no change in VID code within the last 11 μs.
[0] 12V/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 μs. 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 10 and Table 11.
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 outside the
ADT7476A operating temperature range are not possible.