Protocol Conversion Pc File Transfer Summary - IBM 3708 Description

Protocol Conversion PC File Transfer Summary
The following summarizes the scenario for PC file transfer in the 3708's protocol
conversion mode:
• The PC reads a "screen" of data off its diskette for transmission to the host. If
an entire screen (1920 characters) of data is to be transferred, the PC should
have scrolling turned off.
Any file that can contain control characters must be encrypted. Binary files
must be encrypted. 8-bit data transfer is not possible.
• The PC transmits its screen of data to the 3708 followed by an AID key
sequence.
• Upon processing the AID key sequence, the 3708 transfers the screen of data to
the host.
• The host recognizes the AID key as signaling a screen full of data.
• After processing the data, the host updates the screen (perhaps by blanking out
the screen or placing some character sequence in a reserved field) to indicate
whether the data was stored or that the screen needs to be retransmitted.
• The PC recognizes the updated screen and either retransmits its data or sends
the next screen of data.
• This continues until the entire file has been uploaded (a different AID key could
signal the end of file transfer).
• If during transmission, a parity or framing error occurs, the PC program can
either:
Have previously transmitted an Enable File Transfer key sequence
Detection of the parity or framing error is then the responsibility of the host
program.
Recognize that a parity or framing error has occurred (interrogate the status
line), unlock the keyboard by transmitting a RESET key sequence, and
retransmit the data in error.
The algorithm for the host program is similar:
1. The host transmits a screen of data to the PC.
2. Within this screen of data is an indication in a reserved field that tells the PC
that the entire screen has been sent.
3. The PC must recognize and interpret the 3708's Set Cursor Address commands
so that they are not stored on the diskette.
4. If the data was received correctly, the PC stores the data on its diskette and send
an AID key to the host asking for the next screen of data.
5. If the data was received in error, the PC could either request retransmission
from the 3708 by issuing a REFRESH key sequence or by requesting the host to
retransmit via an AID key.
D-8
IBM 3708 Description