2009-06-20bn

This document describes the protocol for the ultrasound fill-meter USF 1000 S.

Datagram is of FS20 sensor message type:

81 0C 04 ?? 01 01 A0 01 A5 CE AA 00 cc xx

81: 		begin of FS20/FHT communication
0C: 		remaining length of datagram (12 bytes)
04: 		type of datagram
??: 		checksum
01 01 A0 01: 	FS20 fix sequence, always 01 01 A0 01
A5 CE: 		FS20 housecode, always A5CE
AA: 		FS20 command, always AA
00:		always 00
cc:		code, see below
xx:		measured distance in cm

code:

	hex	bin
	37	00110111	30min message interval, normal operation
	B7	10110111	3s message interval, normal operation
	F7	11110111	3s message interval, battery low
		|||+++++-- 0x17 always 0x17
		||+------- 0x20 always 1 (= value byte follows)
		|+-------- 0x40 battery warning
		+--------- 0x80 test mode (3s message interval)


measured distance from ultrasound sender/transmitter:

	distance	hex	dec
	0.50 m		0x30	48
	1.00 m		0x60	96
	1.50 m		0x92	146
	2.00 m		0xC4	196

It is assumed that xx is the distance in centimeters from the top of the box
(4 cm box height + 1 cm height of ultrasound sender/transmitter).
