Newtons4th PPA500 - Data Format

PPA5xx/15xx communications manual
1-7
1.4 Data format
Non integer results are sent as ASCII characters in a
scientific format consisting of 5 or 6 digit mantissa plus
exponent:
+1.2345+E00
+1.23456+E00
For higher speed transfer a proprietary binary format can
be selected which compresses the data into 4 bytes, each
of which is sent with the msb set to distinguish them from
ASCII control characters. The data is sent as a 7 bit signed
exponent, a mantissa sign, and a 20 bit mantissa:
byte
data
1
7 bit signed exponent +63 to -64
2
bit 6 = mantissa sign
bit 5:0 = mantissa bit 19:14
3
mantissa bit 13:7
4
mantissa bit 6:0
The value is coded as a binary fraction between 0.5 and
0.9999…, a multiplier of 2^n and a sign ie:
Value = (mantissa / 2^20) x 2^exponent x -1^sign
value
equivalent
hex data transmitted
3.0
0.75 x 2^2
0x82,0xB0,0x80,0x80
0.1
0.8 x 2^-3
0xFD,0xB3,0x99,0xCD
-320
-0.625 x 2^9
0x89,0xE8,0x80,0x80
Any valid number would have the msb of the mantissa set;
any number without the msb of the mantissa set is zero.