Multichannel Selection Operation
11-72
Figure 11–47.
Element Enabling by Subframes in Partitions A and B
112–127
3
80–95
2
48–63
1
16–31
0
0–15
0
96–111
3
64–79
2
32–47
1
0–15
0
0
7
6
5
4
3
2
1
0
FS(R/X)
Partition B
elements
(R/X)PBBLK
Partition A
elements
(R/X)PABLK
Subframe #
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
Transmit data masking allows an element enabled for transmit to have its DX pin
set to the high-impedance state during its transmit period. In systems where sym-
metric transmit and receive provides software benefits, this feature allows trans-
mit elements to be disabled on a shared serial bus. A similar feature is not needed
for receive, because multiple receptions cannot cause serial bus contention.
Note:
DX is masked or driven to the high-impedance state.
-
During inter-packet intervals
-
When an element is masked regardless of whether it is enabled
-
When an element is disabled.
Following are descriptions of how each XMCM value affects operation:
-
XMCM = 00b: The serial port transmits data over the DX pin for the number
of elements programmed in XFRLEN1. Thus, DX is driven during transmit.
-
XMCM = 01b: Only those elements that need to be transmitted are se-
lected via XP(A/B)BLK and XCER. Only these selected elements are writ-
ten to DXR and ultimately transmitted. In other words, if XINTM = 00b,
which implies that an XINT is generated for every DXR-to-XSR copy, the
number of XINT generated is equal to the number of elements selected
via XCER (and
not equal to XFRLEN1).
-
XMCM = 10b: All elements are enabled, which means all the elements in
a data frame (XFRLEN1) are written to DXR and DXR-to-XSR copies oc-
cur at their respective times. However, DX is driven only for those ele-
ments that are selected via XP(A/B)BLK and XCER and is placed in the
high-impedance state otherwise. In this case, if XINTM = 00b, the number
of interrupts generated due to every DXR-to-XSR copy would equal the
number of elements in that frame (XFRLEN1).