Functional Description
ID TECH’s MagChip has two input pins for the
connection of a magnetic read head. The head
signals are amplified by MagChip using an
auto-scaling amplifier. The amplified signal
is used to decode the magnetic stripe signal
(dual-frequency data encoded using the
principals of Aiken’s F2F encoding) into a
digital data format consisting of the
magnetic stripe data, clock, and “media
detect” outputs, all of which are CMOS level
signals. Additionally, MagChip has a
automatic power-down sleep mode that saves
energy. The F2F data rate ranges from less
than 200 to greater than 30,000 magnetic
flux reversals per second, depending upon
data density and the velocity at which the
magnetic stripe is passed across the “read”
head. One clock pulse is required for each
data bit, and the “media detect” signal is
held true while magnetic head signals are
present.
Data Output
Data output is a serial stream of digital
bits, the level of which, with the
corresponding clock, represents each data
bit that was recorded on the magnetic stripe
track. No data filtering is required, as the
first 6 to 9 bits (after MagChip wake-up)
from the leading edge of a magnetic stripe
are not provided as output. These bits are
used for circuit synchronization. A data
output high level is a ZERO value data bit,
and a low level is a ONE value data bit. The
data output is last-bit-first when media is
passed by the head in a reverse direction.
Clock Output
Clocking output is normally high, and goes
low to indicate a data sample time. The data
output is stable and may be sampled on the
falling or rising edge of clock, or at any
time while the clock is low. The MagChip
clock goes low approximately 2 μsec after
the data output is valid. The clock width
changes with speed. (Please refer to the AC
Characteristics table for minimum/maximum
signal timing.) The receiving interface for
MagChip data must sense the high-to-low
clock transition (leading edge) and acquire
the data bit level during clock pulse.
“Media Detect” Output
This output indicates the presence of
encoded magnetic media passing the read
head. This signal is normally high; a low
output indicates encoded media. The output
is an open drain type with high impedance;
the outputs of several MagChip circuits can
be connected together. A pull-up resistor is
needed for proper operation of this output
if it is to be used.
Sleep Mode Function
The MagChip will automatically enter a
power-down sleep mode when a magnetic head
signal is not present. The MagChip will
automatically wake-up when a magnetic head
signal is present. The outputs Data, Clock,
and Media Detect are at a high level during
sleep mode. |
