MagTek MCP - Manual (Page 13)

7
SECTION 3. TRANSPORT FRAME TYPES
I-FRAMES
This section defines the I-frames used in the MCP communications protocol. An I-frame
(information frame) carries an application message in the data field. Application messages are
transparent to this protocol. Application messages are outside the scope of this document. This
section defines the PCB and data fields of the I-frame.
PCB of I-frames
Below is the diagram of the PCB field in the frame header of I-frames:
7 6 5 4 3 2 1 0
FT FT
0 0
ET ET CI RFU N(S) N(R)
MSB LSB
• FT
Frame Type (2 bits) = 00
• ET
EDC Type (2 bits)
• CI
Chain indicator (1 bit)
• N(S)
Send sequence number (1 bit)
• N(R)
Receive sequence number (1 bit)
Frame Type (FT)
The I-frame is designated as frame type 00 (two most significant bits in PCB).
EDC Type (ET)
Error detection code used for the whole frame. The following table defines the possible values:
Value Definition
00 No EDC
01 16-bit CRC (Cyclic Redundancy Check)
10 8-bit LRC (Longitudinal Redundancy Check)
11 Reserved for future use
Chain Indicator (CI)
The chain indicator is not currently supported and must be set to zero.