User`s guide

Aironet Wireless Communications, Inc. 8-2 Confidential and Proprietary
can be made reliable by design since the cable lengths are short. The normal transport layer protocols
used in network operating systems are therefore sufficient for reliable transport of application frames. A
host application (or driver) may choose to occasionally send a SYNC_REQ frame to verify cable
connectivity still exists by the receipt of a SYNC_ACK frame.
Note:
BUSY_OUT line controlled by host PC
BUSY_IN line controlled by PC4500/4800
Autobaud Sequence
In order for the PC4500/4800 to determine which baud rate that the host PC is using, a known sequence
of characters must be transmitted from the host PC to the PC4500/4800. Upon correct recognition of this
sequence, the PC4500/4800 will fix its baud rate to the identified rate. The autobaud sequence is
<CR><CR><CR><3> (<0x0d><0x0d><0x0d><0x33>).
PLAP Synchronization
Two PLAP layers connected by a peripheral line must ensure that they have frame synchronization in
both directions. Since there is no special character used to delineate frame boundaries, correct
synchronization is determined by the successful reception of frames and by the handshake lines of the
interface.
Synchronization should be verified immediately after the autobaud sequence has been sent.
Synchronization should also be checked periodically (every 5 - 60 seconds) if no data has been received
from the remote end during that interval. This check serves as a double check that the other end is still
there and active.
To verify synchronization, a host node sends a SYNC_REQ frame and waits for the SYNC_ACK frame
to be received. If the SYNC_ACK frame is not being received within 1 second, another SYNC_REQ
should be sent. Normally, the PC4500/4800 sends a SYNC_ACK immediately, however, there may be
other processes running which can delay the response. (This is true of host devices in which operating
systems occasionally take time to store its current state and as well as the PC4500/4800 may be
performing a higher priority task and not able to immediately begin a serial transmission.)
Receiving/Transmitting Frames
To transmit a frame the host must first check the BUSY_IN line. If the BUSY_IN line is not active, the
host must first activate the BUSY_OUT line before transmitting the PLAP frame. The host must keep
the BUSY_OUT line active while transmitting the PLAP frame and deactivate the BUSY_OUT line after
the frame is transmitted. On reception of frames, the host should accept the frames only if BUSY_IN is
active. If the BUSY_IN line becomes inactive at any time other than the end of a frame, the frame
reception should be aborted and PLAP re-armed to wait for the start of the next frame.
PLAP Frame Format
The PLAP frame starts with a Frame Type character followed by the frame length. After the frame
length can be several fields/parameters of data. Immediately following the data is the checksum and the
closing character.