71M6543GHT-IGTSLASHF datasheet(63/75 Pages) MAXIM

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71M6543GT/71M6543GHT

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Reading the Info Page

Information useful for calibrating the temperature sensor

and other functions is available in trim fuses. The trim

fuse values provided in the 71M6543T and 71M6543GT

devices cannot be directly accessed through the I/O

RAM space. They reside in a special area termed the

Info Page. The MPU gains access to the Info Page by

setting the INFO_PG (I/O RAM 0x270B[0]) control bit.

Once this bit is set, Info Page contents are accessible

in program memory space starting at the address speci-

fied by the contents of CE_LCTN[6:0] (71M6543GT) or

CE_LCTN[5:0] (71M6543T) (I/O RAM 0x2109[6:0] for

71M6543GHT or 0x2109[5:0] for 71M6543HT). These

pointers specify a base address at a 1KB address bound-

ary, which is at 1024 x CE_LCTN[6:0] (71M6543GT) or

CE_LCTN[5:0] (71M6543T). Table 14 lists of the avail-

able trim fuses and their corresponding offsets relative

to the Info Page base address. After reading the desired

Info Page information, the MPU must reset the INFO_

PG bit.

The code below provides an example for reading Info

Page fuse trims. In this code example, the address, px

is a pointer to the MPU’s code space. In assembly lan-

guage, the Info Page data objects, which are read-only,

must be accessed with the MOVC 8051 instruction.

In C, Info Page trim fuses must be fetched with a pointer

of the correct width, depending whether an 8-bit or a

16-bit data object is to be fetched. The case statements in

the code example below perform casts to obtain a pointer

of the correct size for each object, as needed.

In assembly language, the MPU has to form 11-bit or

16-bit values from two separate 8-bit fetches, depending

on the object being fetched.

The byte values containing less than 8 valid bits are LSB

justified. For example Info Page offset 0x90 is an 8-bit

object, whose three LSBs are bits [10:8] of the complete

TEMP_85[10:0] 11-bit object. The Info Page data objects

are 2’s complement format and should be sign extended

when read into a 16-bit data type (see case _TEMP85 in

the code example).

#if HIGH_PRECISION_METER

int16_t read_trim (enum eTRIMSEL select)

{

uint8r_t *px;

int16_t x;

px = ((uint16_t)select) + ((uint8r_t

*)(CE3 << 10));

switch (select)

{

default:

case _TRIMBGD:

INFO_PG = 1;

x = *px;

INFO_PG = 0;

break;

case _TRIMBGB:

INFO_PG = 1;

x = *(uint16r_t*)px;

INFO_PG = 0;

break;

case _TEMP85:

INFO_PG = 1;

x = *(uint16r_t*)px;

INFO_PG = 0;

if (x & 0x800)

x |= 0xF800;

break;

}

return (x);

}

#endif //#if HIGH_PRECISION_METER

Table 14. Register and Fuses for Temperature Sensing

NAME

DEFINITION

LOCATION

ADDRESS

FORMAT

TYPICAL

VALUE

STEMP_T85_P

STEMP at +85C

Info Block

0xAA, 0xAB

16 bits, signed

4400

STEMP_T22_P

STEMP at +22C

Info Block

0x8A, 0x8B

13 bits, unsigned

3600

T85_P

Probe temperature at

+85C

Info Block

0xA6, 0xA7

16 bits signed

605

T22_P

Probe temperature at

+22C

Info Block

0x9A

8 bits signed

TEMP_85 †

STEMP trim for high

accuracy (H) parts

Info Block

0x90, 0x91

11 bits, sign extended

STEMP

Temperature sensor

I/O RAM

0x2882, 0x2882

11 bits, sign extended

† Not used for temperature sensing. Used for VREF compensation in high accuracy parts.

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