TallyGenicom T2265, Maintenance Manual

Page: 22 / 190

General Functional Description
3-2
3.1.4
Data Transfer
The main difference between the serial and parallel interface is the form in which the
data bytes are transfered. The serial interface transfers bits in a row, one after the
other. Theoretically you only need three connections for this form of data transfer. In
the parallel interface the data transfer of the 8 bits (1 byte) is completed simultane-
ously through 8 parallel connections. At least 11 connections between the computer
and the printer are necessary for this procedure.
With the parallel Centronics interface data up to 100.000 bytes /seconds theoretically
can be transfered. Actually the printer opperates with a maximum transfer frequency
of approx. 30.000 bytes/second. This “Data Flow”, depending on the adjustment of
the input buffer (0-128 KB) on your printer, can be temporarily stored.
3.1.5
Monitoring
The most important functions are monitored with sensors, microswitches and electri-
cal monitoring circuits. These are constantly checked, processed by an internal logic
and indicated on the display.
To prevent an overheating of the printhead, 12 coils of the 24 electromagnets are mo-
nitored. If the temperature reaches a value above 130 °C the speed of the printer is
automatically slowed down. As soon as the printhead has cooled the printer works
with high speed again.
If a coil becomes defective, this is recognized by the firmware and shown on the dis-
play (Head defect, THS Error, Head Hot permanently).
Obviously a worn out print head may cause “Head Hot” message as well.
For safety reasons the top cover is also monitored. If you should open the top cover
during printing operation, then the printout is momentary stopped (to avoid injuries).
When you close the cover again the printout is continued without loss of data.