
C165H
IOM-2 Interface Controller
Data Sheet
320
2001-04-19
PRELMNARY
-EXCERPT-
BAC
if there is more than one HDLC controller connected. This arbitration mechanism is
implemented in the C165H and will be described in the following chapter.
Note:
D-channel access control is only necessary if several D-channel controllers try to
access the same space on the IOM-2 bus.
Note:
The TIC Bus D-Channel Access Control mechanism, as described in
Chapter 14.4.4.1, is implemented for HDLC-2 controller only.
14.4.4.1
TIC Bus D-Channel Access Control for HDLC-2 Controller
The TIC bus is implemented to organize the access to the layer-1 functions of the
transceiver device via IOM-2 interface (C/I-channel) and to the D-channel from up to 7
external communication controllers.
The arbitration mechanism is implemented in the last octet in IOM channel 2 of the IOM-2
interface (IOM-2 TE Mode only, TIC_DIS in IOM_CR is disabled). An access request to
the TIC bus may either be generated by software (MP access to the C/I channel) or by
the C165H itself (transmission of an HDLC frame in the D-channel). A software access
request to the bus is effected by setting the BAC bit (CIC_CMD register) to ’1’.
In the case of an access request, the C165H checks the Bus Accessed-bit BAC (bit 5 of
DU last octet of channel 2) for the status "bus free“, which is indicated by a logical ’1’. If
the bus is free, the C165H transmits its individual TIC bus address TAD programmed in
the CIC_CMD register and compares it bit by bit with the value on DU. If a sent bit set to
’1’ is read back as ’0’ because of the access of another D-channel source with a lower
TAD, the C165H withdraws immediately from the TIC bus. The TIC bus is occupied by
the device which sends its address error-free. If more than one device attempt to seize
the bus simultaneously, the one with the lowest address wins and starts D-channel
transmission.
Figure 111
Structure of Last Octet of Ch2 on DU
DU
tic_octet-du.vsd
B1
B2
MON0
IC1
IC2
MON1
CI1
CI0
D
BAC
TAD
MX
MR
MX
MR
TAD
2
0
1
TIC-Bus Address (TAD 2-0)
Bus Accessed ('1' no TIC-Bus Access)