MagTek MCP - Manual (Page 30)

MCP Serial Transport Protocol
24
R-frame to I-frame Delay
Due to limited resources in MagTek's RS232 and USB MCP devices, there is a limitation when
receiving back to back packets. This affects the MCP protocol only in the following way. The
device requires that the host delay a minimum of 50ms, after sending an R-frame, before sending
the next I-frame.
This issue can be handled robustly by doing the following.
1) If the host is ready to send the R-frame and the host also has another I-frame to send
within the next 100ms or so, then the host can simply send the I-frame instead of the R-frame.
This I-frame will serve as the acknowledgement of the last I-frame sent by the device. The host
can send this I-frame immediately after receiving an I-frame from the device. This method
speeds up the protocol.
2) If the host sends an R-frame, then start a 50ms timer that will keep the host from sending
another I-frame until the timer expires.
GENERAL NOTATION
In the description of the protocol rules and scenarios below, the following notations are used:
Notation Description
N(S) Send sequence number (any node)
N(R) Receive sequence number (any node)
NA(S), NB(S) Send sequence numbers for nodes A and B
NA(R), NB(R) Receive sequence numbers for nodes A and B
NOT N(X) Opposite of N(X) where N(X) can be N(S), N(R), NA(S),
NB(S), NA(R), or NB(R)
I(N(S), N(R)) Non-chained I-frame with send and receive sequence
numbers
R(N(R)) R-frame with poll bit clear
R(N(R))-poll R-frame with poll bit set
S(<cmd> request) S-frame request where <cmd> is the name of the command
S(<cmd> response) S-frame response to the <cmd> request (see above)
S(… request) Any S-frame request
S(… response) Any S-frame response
S(… indication) Any S-frame indication
X(…) Unknown/Invalid frame