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Bad 16 bit Checksum. ‘The Wife’ DMX Tester has confirmed that 16 bit checksums are in
use, but that the checksum did not match the preceding DMX packet. This is an error
condition. Two 16 bit hexadecimal numbers are displayed. The first is the checksum that
‘The Wife’ DMX Tester calculates from the preceding packet. The second number is the
checksum retrieved from the SIP.
SIP data structure
The following table shows the structure of the System Information Packet. Each line of the
table represents a separate display screen on ‘The Wife’ DMX Tester.
NB. The DMX512-A SIP implementation has not yet been ratified by ESTA.
Slot Name
Description
1
Byte Counter
This field represents the number of bytes within the SIP (SIPs
are variable length). Valid values are in the range 24 to 255.
The value is displayed in decimal.
The control bit field contains flags that show whether the SIP
contains checksum information.
The value is displayed in binary. Field values are as follows:
Bit Description
7
Set if MSB of Checksum exists
6
Set if LSB of Checksum exists
5
Reserved and zeroed
4
Reserved and zeroed
3
Reserved and zeroed
2
Reserved and zeroed
1
Reserved and zeroed
2
Control Bit
Field
0
Set to indicate that the receiver should await
packet checksum information prior to using zero
start code information.
3
MSB16
Checksum
The most significant byte of the 16 bit checksum of the previous
packet. SIP’s can include an 8 bit, a 16 bit or no checksum. This
field is only used if the SIP includes a 16 bit checksum.
The checksum is calculated by adding together all 513 slot
values in the previous packet (i.e. include the start code). If this
field is in use, bit 7 & bit 6 of the control bit field will be set.
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