Johnson Controls XT-9100, XP-910x appendix Floating Point Numbers Item List, Examples

Floating Point Numbers

Item List

A DX-9100 floating point number consists of two bytes with following format:

15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
E3	E2	E1	E0	S	M10	M9	M8	M7 M6 M5 M4				M3	M2	M1	M0
where: EEEE									=		4 bits exponent
		S							=		sign (1=negative)
		MMMMMMMMMMM							=		11 bits mantissa

Note: 216 = 32,768; subtracting 4 bits for the exponent, 1 bit for the sign, and 11 bits for the mantissa leaves a maximum value of 2047 for most numeric entries with single digit resolution.

∙A number is normalized when the most significant bit is true (M10 = 1).

∙The value of the n.th mantissa bit (n from 0-10) is:

2 exp -(<EXPONENT>-n)

∙A number is zero when all bits of the mantissa are 0.

∙The value of a number is:

<NUMBER> = <SIGN> * .<MANTISSA> * 2 exp <EXPONENT>

Examples:

1	=	1400H	or	B001H
-1	=	1C00H	or	B801H
100 =		7640H	or	B064H

Symbols used in the Item List:

DI. Decimal Item Address

HI. Hexadecimal Item Address

Type Item Type

R/W Read Write conditions:

R	Read only Item
R/W	Read/Write Item
R/W (E)	Read/Write Item (EEPROM)
CNF	Configuration Item (EEPROM)

Tag Label for Item or bit written within an Item

Configuration Guides—XT-9100 Configuration Guide 25