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<strong>PK</strong>-<strong>232</strong> OPERATING MANUAL<br />
PACKET RADIO<br />
The least significant bit of each byte is used to show whether or not the<br />
byte is the final byte in the address field, as in standard AX.25. The<br />
bits “x” and “y” (lower case) have the function of command and response,<br />
similar to the function of the standard AX.25 version 2.0 SSID byte C bits<br />
(see AX.25 Protocol version 2.0, section 2.4.1.2).<br />
In the Timewave implementation of Lite addressing, the standard callsigne<br />
are compressed to yield short addresses. The destination callsign is<br />
compressed into bit:a A-M, and the source into N-Z. These bits are used<br />
as the address field suggestion following the control byte in the Connect<br />
(SARH) frame. When the bits are used following the control byte as an ID<br />
suggestion or a real extended ID, the format is:<br />
0 A B C D E F G 0 0 H I J K L M 0 N 0 P Q R S T 0 0 u v w x Y Z<br />
If we label the 7 standard right-justified callsign bytes 1-6 and SSID,<br />
here is how we derive the first group of address-bits A-M:<br />
ABCDE = (byte 1 XOR byte 4) AND $1F<br />
FGHI = (byte 2 XOR byte 5) AND $0F<br />
JKLM = (byte 3 XOR byte 6 XOR SSID) AND $0F<br />
Timewave firmware derives the second group of bits N-Z the same way.<br />
Other implementations are free to select any combination of 26 bits when<br />
setting up the short address in either the initial SABM frame or its UA<br />
response.<br />
4.11 Packet Meteor Scatter Extension<br />
A new packet protocol extension has been added for meteor scatter work<br />
that allows a Master/Slave packet connection to be established. This is<br />
done to reduce the possibility of simultaneous transmissions by both sides<br />
of a packet connection over a long meteor scatter path.<br />
This experimental protocol is activated by turning User SIT 18 ON (UBIT 18<br />
ON). When UBIT 18 is ON (default OFF) the packet station that initiates a<br />
packet connect will become the Master station and the station that<br />
acknowledges the connect becomes the Slave.<br />
After a Meteor Scatter connection has been established, the Master station<br />
will continually send either information frames (I-frames) or polling<br />
frames and await an acknowledgment from the slave. The Master station<br />
therefore sends packets constantly, even if all its I-frames have been<br />
acknowledged. The slave station sends nothing, not even I-frames, until<br />
it receives a polling frame from the master. The Slave station may only<br />
send an I-frame to the Master after a poll frame has been received.<br />
2/93 4-31<br />
From The <strong>N3UJJ</strong>.COM Document Library
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