IBM 5251 Series Maintenance Information Manual page 183

MAGNETIC STRIPE READER FEATURE
The Magnetic Stripe Reader (MSR) reads magnetic
stripes on documents such as credit cards or
identification cards. Reading of the magnetic stripe
document is accomplished as follows:
Note: The MSR is positioned with the open portion
(throat) of the slot towards the right.
1.
2.
The operator positions the document so that the
magneti~
stripe is at the bottom of the document
and is facing the operator.
The document is inserted into the throat so that
the bottom of the document is flush against the
bottom surface of the slot plate.
3. The document is moved smoothly and
continuously through the slot from right to left.
The document must remain against the bottom
surface of the slot.
The MSR can read documents from 0.178 to 1.143 mm
(.007 inches to .045 inches) thick at a speed of 127.0 to
1016.0 mm (5 to 40 inches) per second. The MSR can
read at any speed within this range; therefore, a
constant speed through the slot is not necessary.
The MSR contains a document-sensing photocell, a
reading head, and an amplifier. The photocell detects a
document and readies the MSR adapter to receive the 5
bit (4 data bits and 1 parity bit) numeric data from the
MSR. As the data is read from the document, it is
stored in a buffer on the MSR card. Up to 128 bytes
(125 data bytes plus the SOM, EOM, and LRC
characters) can be stored. The MSR card circuits checks
for an error condition and sets the error bit on in all data
bytes if an error is found. Error conditions checked are:
• No SCM, EOM, or LRC characters
• A parity error
• A speed check or LRC check error
The MSR card circuits then sets the service request bit
on. The MPU in the 5251 Display Station Models 1 or
11 or the 5252 Dual Display Station sets the OS
(outstanding status) bit on in the next poll response
frame. The controller then issues a 'read MSR data'
command to read 16 bytes of MSR data. If no error bit
is on in the data received, the above ready sequence
continues until all MSR data has been transferred to the
controller. The MSR card circuits are automatically reset
when the last data is read.
The controller then checks for a missing SOM, EOM, or
LRC character, a parity error, or an LRC error. The MSR
controller also checks to ensure the field is large enough
to accept the data and that an operator ID is not being
read into a field that is not-specified for an operator ID.
When all the checking is complete and the MSR data is
valid, the controller uses a 'write data and load cursor'
command to transmit each byte of data to the 5251
Display Station Models 1 or 11 or the 5252 Dual Display
Station. The display station loads the data into the
regen storage area ready for the display. If an error bit
is on in any data bytes received, the controller stops
reading the data, resets the MSR card circuits, and
displays the appropriate error code. If the controller
detects an error after all data has been received, it
discards the data and displays the appropriate error
code.
Features 5251 MIM 5-3