Series EJ, ET, EY, FJ & FR
102002-177 Rev M2
47
\1020\02177M2.doc 17 Jun 2019
An example will illustrate how the ASCII data protocol is used. Assume that the
Customer computer sends a command to the power supply that sets the analog power
supply parameters to 55% Vmax, 25% Imax, and asserts the digital HV Off control.
The following 18 byte packet will be sent:
The first byte will contain the ASCII character SOH, which will be sent as
01 hex = 0000 0001 binary (enter CTRL-A at the computer keyboard).
Byte 2 is the Set Power Supply command identifier character S. In ASCII, this is 53
hex = 0101 0011 binary (enter capital S at the computer keyboard).
Bytes 3 through 5 represent the voltage, 55% of full scale. Full scale with 12 bit
resolution is FFF hex. 55% is therefore represented as 8CC hex (within an error of 1
lsb). Bytes 3-5 will be sent containing the ASCII representation of 8CC hex (enter
8CC at the computer keyboard):
Byte 3: 38 hex = 0011 1000 binary
Byte 4: 43 hex = 0100 0011 binary
Byte 5: 43 hex = 0100 0011 binary
Bytes 6 through 8 represent the current, 25% of full scale. Full scale with 12 bit
resolution if FFF hex. 25% is therefore represented as 3FF hex (within an error of 1
lsb). Bytes 6 – 8 will be sent containing the ASCII representation of 3FF hex (enter
3FF at the computer keyboard):
Byte 6: 33 hex = 0011 0011 binary
Byte 7: 46 hex = 0100 0110 binary
Byte 8: 46 hex = 0100 0110 binary
Bytes 9 through 14 are not implemented, and all are set to 30 hex = 0 decimal.
Start of message character (“SOH” character: hex 01)
Command Identifier Character (S character, hex 53)
Voltage command (0 – Vmax corresponds to 0 – FFF hex)
Current command (0 – Imax corresponds to 0 – FFF hex)
Digital control data (HV On, HV Off, Power Supply Reset)
Modulo 256 Checksum of all previous bytes except start character
End of message character (carriage return, hex 0D)
Table 6. SET Command Byte Contents
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