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The master sets parameters in the chiller by sending one of the Set Functions as shown in Table 1. The master
does not send a qualifier byte in the data field. The master should be preprogrammed to send the correct
precision and units (it could also read the parameter of interest first to decode the correct precision and units
needed).
For example, if the master wants to set the setpoint to 30°C, it would send :
The chiller responds:
CA 00 01 F0 03 01 00 1E EC
Table 1 Commands (All bytes are in hex)
FUNCTION
Read Acknowledge
Read Status (see Table 3)
Error
Read Internal Temperature (RTD1)CA 00 01 20 00 DE
Read Setpoint (control point)
Read Low Temperature Limit
Read High Temperature Limit
Read Cool Proportional Band (P) CA 00 01 74 00 8A
Read Cool Integral (I)
Read Cool Derivative (D)
Set Setpoint (control point)*
Set Low Temp
Set High Temp
Set Cool Proportional Band
(P = 0.1 - 99.9)
Set Cool Integral (I = 0 - 9.99)
Set Cool Derivative (D = 0 - 5.0)
command bytes shown in bold
qb = qualifier byte, see Table 2
d1,d2 = 16 bit signed integer of the value being
sent or received
cs = the checksum of the string (see text)
Thermo Scientific
command byte
CA 00 01 F0 02 00 1E EE
2 bytes to follow
command byte
3 bytes to follow
MASTER SENDS
CA 00 01 00 00 FE
CA 00 01 09 00 F5
CA 00 01 70 00 8E
CA 00 01 40 00 BE
CA 00 01 60 00 9E
CA 00 01 75 00 89
CA 00 01 76 00 88
CA 00 01 F0 02(d1)(d2)(cs)
CA 00 01 C0 02(d1)(d2)(cs)
CA 00 01 E0 02(d1)(d2)(cs)
CA 00 01 F4 02(d1)(d2)(cs)
CA 00 01 F5 02(d1)(d2)(cs)
CA 00 01 F6 02(d1)(d2)(cs)
The checksum is the bitwise inversion of
11 (00+01+F0+02+00+1E) =111
Take the LSB = 11
The temperature of 30°C is 30 decimal = 001E hex.
The qualifier byte of 01 indicates a precision of 0
decimal point and units of °C. The temperature of
30°C is 30 decimal = 001E hex.
The checksum is the bitwise inversion of 13
(00+01+F0+03+01+00+1E)
Take the LSB = 13
CHILLER RESPONDS
CA 00 01 00 02(v1)(v2)(cs)
CA 00 01 09 02(d1)(d2)(cs)
CA 00 01 0F 02(en)(ed)(cs)
CA 00 01 20 03(qb)(d1)(d2)(cs)
CA 00 01 70 03(qb)(d1)(d2)(cs)
CA 00 01 40 03(qb)(d1)(d2)(cs)
CA 00 01 60 03(qb)(d1)(d2)(cs)
CA 00 01 74 03(qb)(d1)(d2)(cs)
CA 00 01 75 03(qb)(d1)(d2)(cs)
CA 00 01 76 03(qb)(d1)(d2)(cs)
CA 00 01 F0 03(qb)(d1)(d2)(cs)
CA 00 01 C0 03(qb)(d1)(d2)(cs)
CA 00 01 E0 03(qb)(d1)(d2)(cs)
CA 00 01 F4 03(qb)(d1)(d2)(cs)
CA 00 01 F5 03(qb)(d1)(d2)(cs)
CA 00 01 F6 03(qb)(d1)(d2)(cs)
v1. v2 = protocol version
ed Bad command byte gets echoed)
en (error number) 01 = Bad command,
xx = no valid data, include in checksum
Appendix
02 = Bad checksum
Merlin A - 3
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