Rainbow Electronics DS1841 - Manual (Page 7)

DS1841
Temperature-Controlled, NV, I 2 C,
Logarithmic Resistor
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LUT Adder Mode (Default)
LUT Adder Mode is selected by setting the Update
Mode bit to 1 and the Adder Mode bit to 1. This mode
operates similar to LUT Mode with one major difference
(see the
LUT Mode and LUT Adder Mode Block
Diagram ). The WR is loaded with the sum of the values
of LUTVAL (the value pointed to by the address stored
in LUTAR) and IVR. Furthermore, in this mode, the val-
ues programmed into the LUT are signed two’s com-
plement. This allows convenient positive or negative
offsetting of the nominal IVR value. WR resistance val-
ues clamp at 00h and 7Fh (the MSB is ignored).
LUT Mode
LUT Mode is selected by setting the Update Mode bit
(Control Register 1, address 03h, bit 0) to a 1 and the
Adder Mode bit (Control Register 1, address 03h, bit 1)
to a 0. An overview of the DS1841 in this mode is illus-
trated in the
LUT Mode and LUT Adder Mode Block
Diagram . The memory map for the LUT Mode and the
LUT Adder Mode is shown in Table 2. The major differ-
ence between the two LUT modes is whether the value
in the IVR is added to the values stored in the LUT. The
dashed line/arrow shown in the
LUT Drive Mode Block
Diagram is not active in LUT Mode. When in LUT Mode,
on power-up the IVR value is recalled into the WR. This
value remains there until completion of the first temper-
ature conversion following power-up. The temperature
is measured every t
FRAME . The temperature value is
used to calculate an index that points to the corre-
sponding value in the LUT. This index is referred to as
the LUT Address Register (LUTAR) and is located at
address 08h. The value stored in the LUT at the loca-
tion pointed to by LUTAR is called LUTVAL, and this
value is stored as the WR value (WR) at address 09h
when Update Mode bit = 1. The process then repeats
itself, continuously updating the wiper setting in a
closed-loop fashion. In this mode the 72-byte LUT is
populated with wiper settings for each two-degree tem-
perature window. Valid wiper settings are 00h to 7Fh
(the MSB is ignored). Table 3 shows the memory
addresses of the LUT as well as the corresponding
temperature range for each byte in the LUT.
Table 2. LUT Mode and LUT Adder Mode Memory Map
*In LUT Mode and LUT Adder Mode, WR is accessed through memory address 09h, while IVR remains at memory address 00h.
REGISTER NAME
ADDRESS
(HEX)
VOLATILE/NV
FACTORY/POWER-UP
DEFAULT
IVR Initial Value Register 00h NV (Shadowed) 00h
CR0 Control Register 0 02h Volatile 00h
CR1 Control Register 1 03h NV (Shadowed) 03h
LUTAR LUT Address Register 08h Volatile 00h
WR LUT Value Register 09h* Volatile 00h
CR2 Control Register 2 0Ah Volatile 00h
TEMP Temperature Result 0Ch Volatile (Read Only) N/A
VOLTAGE Supply Voltage Result 0Eh Volatile N/A
LUT
Temperature Lookup
Registers
80h–C7h NV 00h