HP HP-97 User Manual

Theory
of
Operation
HP-97
a set of comparators, A1 through A4. A1 compares the motor output voltage
with a reference voltage derived within U5. If the motor is going too slow,
its output voltage will be less than the reference voltage. The A1
comparator instructs the PIK to speed up the motor. The PIK then changes
the FWD signal pulse width to accomplish this. This operation occurs only
during forward head movement. If the head is moving too fast, again the
comparator output will change and the FWD signal pulse width will change to
compensate.
2-32. Print Intensity Control
2-33. To maintain uniform print contrast, each head resistor must be
energized to the same temperature, independent of battery voltage changes.
2-34. The remaining comparators in U4, along with the resistor network
in U5, produce the variable duty-cycle signal STB, which is nominally 10
kHz.The STB signal will change its duty-cycle to keep its rms value con-
stant and thus print intensity constant. By changing the value of R8, the
nominal duty-cycle of STB can be changed to adjust print intensity.
2-35. CARD READER
2-36. When a card is inserted into the card reader, the motor switch is
closed, grounding the MTRS signal. This signal is fed to the CRC, which
tells the microprocessor (contained in the ROM's and ACT) that a card is in
the card reader. The microprocessor in response tells the CRC to turn on
the card reader motor. The CRC then grounds the MOTOR signal to the sense
amp, which supplies power to the motor. The motor turns a roller, which
passes the card through the card reader.
2-37. When the leading end of the card reaches the card reader head, the
head switch is closed, grounding the HDS signal. For a read operation,
flux transitions on the card are picked up by the head, amplified and
converted to digital levels by the sense amp, buffered by the ACT, and
then passes to the appropriate data storage registers. For a write operation
this process is reversed. The microprocessor informs the CRC whether the
operation is a read or write.
2-38. Information is recorded as a flux transition onto two tracks on each
edge of the card. A header at the beginning of both tracks indicates
whether the information on the card is a program or data. If the card
contains a program, this header also contains flag and display format
information and indicates whether side 1 or side 2 of the program is being
read/written. At the end of the tracks is a checksum, which is used by
the microprocessor to check for errors in reading. If an error is so
detected, the microprocessor generates an "Error" display.
2-8

HP HP-97 Specifications

General

Brand	HP
Model	HP-97
Category	Calculator
Language	English