am79c30a Advanced Micro Devices, am79c30a Datasheet - Page 38

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

If DMR4 bit 6 is set to a logical 0, bit 1 of the FRARs is
ignored when matching the first incoming address byte.
If DMR4 bit 6 is set to a logical 1, all bits of the FRARs
are used when matching the first incoming address
byte. FRAR bit 1 is analogous to the C/R bit defined by
the CCITT recommendations. The address recognition
mechanism for the four FRAR/SRAR addresses can be
individually enabled/disabled via DMR1 bits 4–7.
First Received Byte-Only Address Recognition
If DMR4 bit 5 is set to a logical 1 and DMR4 bit 7 is set
to a logical 0, only the first byte of the incoming address
is compared with the values stored in the enabled
FRARs. An interrupt is generated if there is an address
match and the Valid Address interrupt is enabled. If the
address matches, the packet will be received.
Second Received Byte-Only Address Recognition
If DMR4 bits 5 and 7 are set to a logical 1, the DLC
compares only the value in the second byte of the in-
coming address with values stored in the enabled
SRARs. An interrupt is generated if there is an address
match and the Valid Address interrupt is enabled. If the
address matches, the packet will be received.
2-Byte Address Recognition
If DMR4 bit 5 is set to a logical 0, the first byte of the
incoming address is compared with the values stored in
the enabled FRARs, and the second byte of the incom-
ing address is compared with the value stored in the
corresponding SRAR. An interrupt is generated if a
match is found for both incoming address bytes with a
FRAR/SRAR pair and the Valid Address interrupt is en-
abled. If the address matches, the packet will be re-
ceived.
Disabling Address Recognition
If DMR1 bits 4, 5, 6, and 7 are all set to logical 0, all ad-
dress recognition is disabled and all addresses are rec-
38
Bit 7
X
X
0
1
DMR4
Bit 5
1
1
0
X
X
X
X
X
X
X
X
X
7
1
1
1
0
X
X
X
X
X
X
X
X
6
1
1
1
0
DMR1
Bits
X
X
X
X
X
X
X
X
X
5
1
1
0
Table 38. .Address Recognition
X
X
X
X
X
X
X
X
4
1
1
1
0
Am79C30A/32A Data Sheet
FRAR1
FRAR3
FRAR4
SRAR1
SRAR2
SRAR3
SRAR4
FRAR1:SRAR1
FRAR2:SRAR2
FRAR3:SRAR3
FRAR4:SRAR4
ognized and received. In this case, the Am79C30A/32A
receives the first two bytes following the opening flag
(the incoming address), and then issues an End of Ad-
dress interrupt if the End of Address interrupt is enabled.
DLC Operation
DLC Transmit and Receive FIFOs
The DLC Transmit and Receive FIFOs may be config-
ured to the Normal or Extended mode of operation.Nor-
mal mode is fully backwards compatible with the
Revision D or prior DSC circuit, and is activated upon
RESET or if EFCR bit 0 is programmed to logical 0. In
Normal mode the Transmit and Receive FIFOs are
each 8 bytes in length.
The Extended mode of FIFO operation may be activated
by programming EFCR bit 0 to a logical 1, increasing the
depth of the Transmit and Receive FIFOs to 16 bytes
and 32 bytes, respectively. The setting of EFCR bit 0 to
logical 1 also alters the available programmable FIFO
threshold values set by DMR4 bits 2 and 3.
Receiving D-Channel Packets
The receiver controls the flow of D-channel data to the
D-channel Receive buffer and the termination of a re-
ceive packet. Up to two packets can be contained in the
D-channel Receive buffer.
After receiving an opening flag (a bit sequence of
01111110) and one byte of data which is not an abort
or flag on the D channel, the DLC sets the Packet-Re-
ception-in-Progress status bit (bit 2) in D-channel Sta-
tus Register 1 (DSR1). The DLC then receives the first
two bytes (the two address bytes). If address recogni-
tion is enabled, the Am79C30A/32A issues a Valid Ad-
dress interrupt if a match between the programmed
values and the received address is detected. If no
match is detected and address recognition is enabled,
the DLC ignores the packet. If address recognition is
Type of address recognition
First received byte-only address
Second received byte-only address
2-byte address
Address recognition disabled