am79c30a Advanced Micro Devices, am79c30a Datasheet - Page 50

• Manufacturer Part Number: am79c30a
• Description: Digital Subscriber Controller ?dsc ?circuit
• Manufacturer: Advanced Micro Devices

DSC/IDC Circuit IOM-2 Terminal Mode
Implementation
Data Channels
The B1 and B2 channels are physically the first two
8-bit time slots after the frame sync pulse. When mak-
ing a MUX connection to these channels, IOM-2 chan-
nels B1 and B2 correspond to MUX channels Bd and
Be, respectively. When in an IOM-2 mode, a MUX con-
nection to channel Bf provides access to one of the two
intercommunication channels as selected in PPCR1.
Command/Indicate Channels
The Peripheral Port supports the C/I channels of the
first and second IOM-2 subframes. The Peripheral Port
monitors these two channels, and generates an inter-
rupt any time the received data changes and is stable
for two frames. The received data is read from C/I Re-
ceive Data Register 0 or 1, and C/I transmit data is writ-
ten to C/I Transmit Data Register 0 or 1. When the TIC
bus feature is enabled, C/I0 transmit access to the
IOM-2 Interface is controlled by CITDR0 bit 7, Bus Ac-
cess Request.
D Channel
If the peripheral Port is configured as IOM-2 master
with TIC bus disabled, the DLC will transmit and re-
ceive D-channel data to and from the S Interface
50
Notes:
BAC bit (Bus Accessed): indication to other devices that the TIC bus is being accessed. When 0 the bus is accessed, when 1 it
is free. This bit is driven to zero by the device that gets an address match on the TBA2–0 bits.
TBA2–0 bits (TIC Bus Address): address bit used for arbitration of TIC bus control Assumes Open–Drain bus such that device
with highest zero content in its address has the highest priority. Lowest priority address, which is also the default, is 111.
E-bits (Echo): D-channel Echo bits from the S-bus. Will not be supported by the DSC.
S/G bit (Stop/Go): used to indicate availability of the S-bus D-channel. When 0, the D-channel is clear for transmission. When
1, D-channel transmission should be halted.
A/B bit (Available/Blocked): supplementary bit for D-channel control. 1 indicates D-channel available, 0 D-channel blocked.
Optional, will not be supported by the DSC.
Data Downstream (input)
Data Upstream (output)
Figure 7. TIC Bus Control Bits and Definitions
E
1
Am79C30A/32A Data Sheet
E
1
BAC TBA2 TBA1 TBA0
S/G
through the LIU. The D-channel data received from the
S Interface is also output on the IOM-2 Interface.
D-channel data received from the IOM-2 Interface is
disregarded. If, however, TIC bus is enabled, the TIC
bus control logic will arbitrate D-channel data flow be-
tween the S Interface and either the DLC or IOM-2 In-
terface based on TIC bus access procedures.
When the Peripheral Port is configured as IOM-2 slave,
the DLC will transmit and receive D-channel data to
and from the IOM-2 Interface. This will be a dedicated
path if the TIC bus feature is disabled, or with DLC ac-
cess arbitrated according to TIC bus access proce-
dures if the TIC bus feature is enabled. The LIU is not
used in this situation, so there is no D-channel data
flow between the DLC and LIU.
Monitor Channels
Support for the two Monitor channels is provided on a
one-at-a-time basis. A bit in Peripheral Port Control
Register 1 selects which one of the two Monitor chan-
nels is utilized at any time.
TIC Bus
The IOM-2 TIC bus control bits reside in the last byte to
the IOM-2 Terminal mode frame (channel 2, byte 4).
The bits and their definitions are shown in Figure 7
A/B
1
1
1
1
1
1