
XRT7245
DS3 UNI FOR ATM
á
PRELIMINARY
REV. 1.03
192
DS3 Mask Registers. These “Mask Registers” and
their comprising bit-fields are defined below.
The bit-fields of the Tx DS3 M-bit Mask Register that
are relevant to error-insertion are shaded. The remain-
ing bit-fields pertain to the FEBE bit-fields, and are
discussed in Section 6.4.3.1.4.
The Tx DS3 M-Bit Mask Register serves two purpos-
es
It allows the user to transmit his/her own value for
FEBE (3 bits)—please see Section 6.4.3.1.4.
It allows the user to transmit errored P-bits.
It allows the user to insert errors into the M-bit
(framing bits) in order to support equipment testing.
1.
2.
3.
Each of these bit-fields are discussed below.
Bit 3—Tx Err (Transmit Errored) P-Bit
This bit-field allows the user to insert errors into the
P-bits of each outbound DS3 Frame, for equipment
testing purposes. If this bit-field is “0”, then the P-Bits
are transmitted as calculated from the payload of the
previous DS3 frames. However, if this bit-field is “1”,
then the P-bits are inverted (from their calculated val-
ue) prior to transmission.
Bits 2—0: M-Bit Mask[2:0]
The Transmit DS3 Framer will automatically perform an
XOR operation with the M-bits (in the DS3 data-stream)
and the contents of the corresponding bit-field, within
this register. The results of this operation will be writ-
ten back into the M-bit positions of the outbound DS3
Frames. Therefore, if the user does not wish to insert
errors into the M-bits, he/she must make sure that the
contents of these bit-fields: M-Bit Mask[2:0] are “0”.
F-Bit Error Insertion
The remaining mask registers (Tx DS3 F-Bit Mask1
through Mask4 registers) contain bit-fields which
correspond to each of the 28 F-bits within the DS3
frame. Prior to transmission, these bit-fields are
automatically XORed with the contents of the corre-
sponding bit fields within these Mask Registers. The
result of this XOR operation is written back into the
corresponding bit-field, within the outgoing DS3
frame, and is transmitted on the line. Therefore, if the
user does not wish to modify any of these bits, then
he/she must insure that these registers contain all
“0s” (the default value).
Tx DS3 M-Bit Mask Register, Address = 17h
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
TxFEBE-
Dat[2]
TxFEBE
Dat[1]
TxFEBE
Dat[0]
FEBE Reg
Enable
TxErr PBit
MBit Mask(2) MBit Mask(1) MBit Mask(0)
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Tx DS3 F-Bit Mask1 Register, Address = 18h
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Unused
Unused
Unused
Unused
FBit Mask (27) FBit Mask (26) FBit Mask (25) FBit Mask (24)
RO
RO
RO
RO
R/W
R/W
R/W
R/W
Tx DS3 F-Bit Mask2 Register, Address = 19h
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
FBit Mask
(23)
FBit Mask
(22)
FBit Mask
(21)
FBit Mask
(20)
FBit Mask
(19)
FBit Mask
(18)
FBit Mask
(17)
FBit Mask
(16)
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W