Intermec EasyCoder 7421 User Manual page 76

The printer returns its highest priority status when it receives a
valid block (<STX> data <ETX>) or when it receives the status
request command <ENQ>. When the printer receives the status
dump command (<VT>), the printer returns all active status. The
printer status response time ranges from 30 ms to 100 ms
depending on the complexity of the received message block. In
the case of a transmission error, the printer responds with a
<NAK> and discards the entire message block.
The table below shows printer status conditions in descending
order of priority:
Buffer already full
Ribbon fault
No label stock
Buffer now full
Printhead hot
Label at strip pin
Skipping
Printing
Ready/Online
Note: Do not confuse the Buffer now full <DC3> status with the
XON/XOFF characters <DC1> and <DC3>.
When the printer returns Buffer Now Full (<DC3>) status, it
accepts the currently received message block. At this time, the
printer can accept short messages to allow parsing of immediate
commands such as Reset (<DLE>) or Cancel Batch Printing
(<EM>). However, if the printer responds with a <GS> to any
message block, the buffer is already full and the printer discards
the entire message block. In case of a transmission error, the
printer discards the whole message block and responds with a
Negative Acknowledgment (NAK). You should retransmit the
message block from the host.
GS
US
EM
DC3
SI
FS
DC1
DC1
DC1