MagTek MCP - Manual (Page 17)

Section 3. Transport Frame Types
11
S-FRAMES
This section defines the S-frames used in the MCP communications protocol. An S-frame
(supervisory frame) is used for transmission control; this includes resynchronization, exchanging
communication parameters between nodes, error recovery and flow control.
S-frames must always use the 8-bit LRC error detection method for the entire frame.
This section defines the S-frame PCB, data field and the transmission control commands.
PCB of S-frames
Below is the diagram of the PCB field in the frame header of S-frames:
7 6 5 4 3 2 1 0
FT FT
1 0
STYP STYP CC CC CC CC
MSB LSB
• FT
Frame Type (2 bits) = 10
• STYP S-frame type (2 bits)
• CC
Command Code (4 bits)
Frame Type (FT)
The S-frame is designated as frame type 10 (two most significant bits in PCB).
S-frame Type (STYP)
The following S-frame types are defined (2 bits):
Value Definition
00 Indication
01 Request
10 Response
11
Reserved for future use
Indication S-frames are sent by the node when it discovers a specific condition. There is no
prescription on how the other node should respond.