DEC DECtape 551 Manual page 43

The drivers are returned to -14 volts. Two watt resistors mounted on lugs on the module are
used to I imit the head current and may be changed in order to change this current. Head cur-
rents up to 150 mill iamperes are perm iss ib Ie.
Inputs and Outputs
Complement Input - Standard DEC positive pulses appl ied to pin H at any rate up to 35 kc
cause the write fl ip-flop to compl ement and the current through the head to reverse with each
pulse •
.!!!J. -
A ground level applied to pin K causes the flip-flop to assume a state that permits write
current to flow into pin N when a strobe pulse is applied to pin
J.
A -3 volt level causes the
write current to flow into pin M .
.!!:!2. -
A ground level applied to pin E causes the flip-flop to assume a state that permits write
current to flow into pin M when a strobe pulse is appl ied to pin F. A - 3 volt level causes the
write current to flow into pin N.
Enable - A ground level on pin L disables both current drivers so that no write current flows.
In order to begin writing on tape, pin L must be at - 3 volts.
Strobe 1 - A standard positive pulse applied to pin J reads the data on pin K into the write
fl ip-flop.
Strobe 2 - A standard positive pulse applied to pin F reads the data on pin E into the write
fl ip-flop.
Writer Out - A maximum of 150 mi" iamperes and 14 volts are suppl ied from either pin M or N
depending on the state of the write flip-flop and the enable input.
Reader In - Pins Sand T are the inputs to the read ampl ifier. These pins are usually connected
to pins M and N respectively and to the opposite ends of a center-tapped read-write head.
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