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Glossary
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watchdog timer
A clock on the PC that measures the time it takes the PC program to complete
one cycle. If the cycle time is longer than 100 ms, a warning is issued. If the cycle
time is longer than 130 ms, the PC will suspend operation. The watchdog timer is
reset at the beginning of each cycle.
word
A word is made up of two bytes or 16 bits. The term “word” is used interchange-
ably with the term “data word” to indicate a single unit of data. Blocks of data are
transferred in word units. For data transfer, the address of a data block’s first
word and the number of words to be transferred must be specified.
Write Flag
A PC hardware flag that indicates when data can be written to the PC. When this
flag is set, data can be written to the PC.
XON/XOFF
OPEN statement parameters that control the rate at which the port buffers re-
ceive and transmit data. If the XON command is specified to be ON by the OPEN
statement, then when the port buffer becomes 3/4 full, the ASCII Unit will sus-
pend data transfer until the port buffer is less than 1/4 full. In a case where a
transmitting device is sending data at a faster baud rate than the ASCII Unit is set
for, the XON command will keep the transmitted data from being written over.
Summary of Contents for C500-ASC04
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