Device-Initiated Messages In Slip Format - Magtek mDynamo Programmer's Manual

3 - Data Formats

3.2.1 Device-Initiated Messages In SLIP Format

When using SLIP format, the device may send Notification Messages Sent from Device to Host
(Extended Notifications Only) in either normal or Run-Length Encoded (RLE) compressed format,
depending on whether RLE would help compress the data or not. The host software should understand
both formats. The first byte of the incoming message is a message type field, which indicates what type
of data the device is sending and whether the data is RLE compressed, as follows:
•
0x02 = Notification Uncompressed, which indicates the Notification Data contains an uncompressed
notification message [see section 6 Notification Messages Sent from Device to Host (Extended
Notifications Only)].
•
0x03 = Notification RLE, which indicates the Notification Data contains a run-length-encoded
compressed notification message [see section 6 Notification Messages Sent from Device to Host
(Extended Notifications Only) and the information below about RLE decoding].
The device implements RLE encoding of Notification Message data as follows:
1) Any byte that is repeated more than once consecutively is run length encoded. Bytes that are not
repeated stay as-is.
2) Repeated bytes are run-length encoded by repeating the byte twice, followed by the number of times
the byte was repeated in the original data.
3) The maximum length of an encoded run is 255, so runs larger than 255 bytes are encoded as multiple
runs of 255 bytes each until the last run.
For example, the data 0x44 0x55 0x55 0x55 0x55 0x55 0x55 0x55 0x55 0x055 0x66
0x00 0x00 is encoded as 0x44 0x55 0x55 0x09 0x66 0x00 0x00 0x02. A run of 260
0x00 bytes would be encoded as 0x00 0x00 0xFF 0x00 0x00 0x05.
mDynamo| OEM Secure Card Reader Authenticator | Programmer's Manual (COMMANDS)
Page 25 of 167 (D998200151-200)