pt7a6525 Pericom Technology Inc, pt7a6525 Datasheet - Page 17

• Manufacturer Part Number: pt7a6525
• Description: Pt7a6525/6525l/6526 Hdlc Controller
• Manufacturer: Pericom Technology Inc

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Note: The broadcast address may be programmed in RAL2 if
broadcasting is required.
Half-Duplex SDLC-NRM Operation
In Half-Duplex Normal Response Mode (NRM), the PT7A6526
will operate as a slave (secondary) station by setting the NRM
bit in the XBCH register of the respective channel.
This mode allows transmission of responses only; the slave
station may make a transmission only when instructed to do so
by the master (primary) station.
The permission given by the primary station to transmit a frame
is contained in an S or I frame with the poll bit (p) set.
In the point-to-multipoint configuration with a fixed master-
slave relationship, the NRM mode can be used effectively to
avoid collisions within the common transmission medium. It is
the responsibility of the master station to poll the slave stations
periodically and to manage error recovery.
The required setup for NRM operation is:
PT0017(12/05)
- Auto Mode with 8-bit address field selected
-
-
can be transmitted, i.e.
External Timer Mode
Same transmit and receive addresses; as only responses
MODE: MDS0, MDS1, ADM = 000
XAD1 =XAD2 = RAL1 = RAL2
MODE: TDM = 0
(address of
slave)
17
PT7A6525/6525L/6526 HDLC Controller
• Reception of Frames
The reception of frames functions identically to LAPB/LAPD
operation.
• Transmission of Frames
The device does not transmit S or I frames unless so instructed
by an S or I frame with the poll bit set, sent by the primary
station.
An I frame is readied for transmission in the PT7A6526 by the
microprocessor issuing an XIF command (via CMDR), and the
frame transmission will be initiated when the device receives
either an
with the poll bit set (p = 1).
After the frame has been transmitted (with the final bit set), the
XFIFO is inhibited, and the device waits for the arrival of a
positive acknowledgement.
As the on-chip timer must be operated while in External Mode
(a secondary station may not poll the primary for
acknowledgements), time-supervisory control must be handled
by the primary station.
Upon the arrival of an acknowledgement, the XFIFO is enabled,
and an interrupt is forwarded to the microprocessor when either
- the message has been acknowledged as positive (XPR
- the message must be repeated (XMR interrupt).
Additionally, the timer can be operated under microprocessor
control to provide timer recovery of the slave if no
acknowledgements are received at all.
Note: The transmission of transparent frames is possible only if
permission to send is obtained via an S frame (p = 1) or an I
frame.
Figure 6 shows the transfer of frames between primary station
and slave station.
interrupt), or
- RR, or
- I frame
Data Sheet
Ver:8