First Alert ACTION T-1000 - Manual (Page 67)

Technical
Specifications
The column heading “Direction” refers to the direction of signal flow
as viewed from the printer.
“Return” denotes the twisted-pair return, to be connected at signal
ground level. For the interface wiring, be sure to use a twisted-pair
cable for each signal and to complete the connection on the return
side. To prevent noise, these cables should be shielded and connected
to the chassis of the host computer or the printer but not at both
ends.
All interface conditions are based on TTL level. Both the rise and the
fall times of each signal must be less than 0.2 microseconds.
Data transfer must be carried out by observing the ACKNLG or
BUSY signal. (Data transfer to this printer can be carried out only
after receipt of the ACKNLG signal or when the level of the BUSY
signal is LOW.)
Data Transfer Sequence
Interface timing
The illustration below shows the timing for the parallel interface.
Technical Specifications 6-7