AEA PK-232 Technical Reference Manual page 59

PK-232 TECHNICAL MANUAL
An invalid or not implemented command or response is defined as a frame with a control field that
is unknown to the receiver of this frame.
A.3.4.3.3.2
When a FRMR frame is sent, an information field is added to the frame that contains additional in-
formation indicating where the problem occurred. This information field is three octets long and is
shown in Fig. 9.
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
0 0 0 0
Where
:
1. The rejected frame control field carries the control field of the frame that caused the reject
condition. It is in bits 0-7 of the information field.
2. V(S) is the current send state variable of the device reporting the rejection (bit 9 is the low
bit).
3. The CR bit is set to zero to indicate the rejected frame was a command, or one if it was a re-
sponse.
4. V(R) is the current receive state variable of the device reporting rejection (bit 13 is the low
bit).
5. If W is set to 1, the control field received was invalid or not implemented.
6. If X is set to 1, the frame that caused the reject condition was considered invalid because it
was a U or S frame that had an information field that is not allowed. Bit W must be set to 1 in
addition to the X bit.
7. If Y is set to 1, the control field received and returned in bits exceeded the maximum allowed
under this recommendation in A.4.7.3, below.
8. If A is set to 1, the control field received and returned in bits 1 to 8 contained an invalid N(R).
9. Bits 8, and 20 to 23 are set to 0.
A.3.4.3.4 Unnumbered Acknowledge (UA) Response
The UA response frame is sent to acknowledge the reception and acceptance of a SABM or DISC
command frame. A received command is not actually processed until the UA response frame is
sent. Information fields are not permitted in a UA frame.
A.3.4.3.5 Disconnected Mode (DM) Response
The disconnected mode response is sent whenever a DXE receives a frame other than a SABM or
UI frame while in a disconnected mode. It is also sent to request a set mode command, or to indi-
cate it cannot accept a connection at the moment. The DM response does not have an information
field.
Whenever a SABM frame is a received, and it is determined that a connection is not possible, a DM
frame shall be sent. This will indicate that the called station cannot accept a connection at that
time.
While a DXE is in the disconnected mode, it will respond to any command other than a SABM or UI
frame with a DM response with the P/F bit set to 1.
PK232TM Rev. A 5/87
Fig. 9 – FRMR frame information field
Information Field Bits
Z Y X W
C
V(R) V(S)
R
A-14
APPENDIX A – AX.25 LEVEL 2 PROTOCOL
Rejected Frame
0
Control Field
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