MagTek TRIPLE TRACK Delta ASIC User Manual
Page 8
Triple Track ASIC
4
Prior to issuing track ‘A’ data for the first time following a card swipe, the ASIC issues a “preamble” of
16 bits. This preamble indicates the revision of the ASIC. See
. The preamble is the
first “data” issued following a card swipe and is issued only once per data-extraction routine; it is not
repeated until the chip has been reset, and another swipe is completed.
The ASIC provides two indications for end-of-card (the initial Buffer-Ready state). The primary
indication normally occurs first and is triggered when all awakened tracks have each issued thirteen
consecutive zero-bits starting from 32 bit-cells after the first one-bit for a given track. This primary
indication of end-of-card is the ZEROES FLAG, a high to low transition on the DATA line. The
ZEROES FLAG indication on the DATA line should elicit a response of two low-going pulses from the
user’s controller on the STROBE line. The first of these low-going STROBE pulses is designated the
CLEAR signal, indicating a clearing of the ZEROES FLAG. The second STROBE is designated the
STOP signal, indicating a stopping of analog data collection. After a period of “Tss” (see timing chart
that follows) the ASIC will acknowledge the second low-going pulse of the STROBE by pulling DATA
low (if not already low) to the BUFFER-READY state. This is the “handshake” mentioned earlier. At
this point the ASIC is ready to accept a low-going STROBE pulse for extraction of the first bit of the 16-
bit “preamble”.
Issuing the two “handshake” STROBE pulses upon receiving the ZEROES FLAG allows the user to
begin extracting data as soon as possible, even before the card has finished its swipe past the magnetic
head. This practice combined with a high speed data extraction routine will minimize the time required to
re-arm the ASIC for reading – critical in some applications.
If the card is so badly damaged such that 13 consecutive zero-bits do not exist at the end of the data on all
utilized tracks, then there will be no ZEROES FLAG issued. However, the DATA line will still transition
from high to low to indicate the card’s end. This transition is called the AUXILIARY FLAG and is the
secondary end-of-card indication. In this case, the two low-going STROBE pulses must still be issued as
the “handshake” before data can be extracted. There will be no acknowledgement of either STROBE
pulse on the DATA line in this case. Note that if such a damaged card has one or more 75 bpi tracks and
is used in a high ambient noise environment, under some unlikely conditions the time required to receive
the AUXILIARY FLAG may be as much as from 1.35 to 3.1 seconds from the start of the card swipe.
With the exception of this rare case or a swipe that is so slow as to cause an internal timeout, the ASIC
will issue the AUXILIARY FLAG coincident with the encoded portion of the magnetic stripe losing
contact with the magnetic head gap. If an internal timeout occurs because of an extremely slow swipe, the
buffer will not be cleared, but will contain all data up to the point of the timeout. An internal timeout may
occur because of too slow of a swipe speed for a single bit, or for the aggregate time elapsed for the
swipe.
If the card being decoded has less than 13 consecutive zero-bits at the end of the swipe as described
above, then there may be some extraneous noise bits at the end of the ASIC’s buffer. Firmware should
anticipate the possibility of these extraneous bits.
The STROBE pin is edge triggered. Thus, for example, if the controller for some reason is holding
STROBE low when DATA indicates the ZEROES FLAG, the controller must take STROBE high and
then low again to issue the first of the two handshake STROBE signals required. It is recommended that
STROBE be kept high when not in the state of “BUFFER-READY” to maintain compatibility with future
products. It is also recommended that STROBE be held in a high state at power-up.