The standard defines
20 switching patterns for the ABMs. Although the number of analog switches in
this structure is smaller than in the TBIC, we now have twice the number of
switch conditions. This fact reflects the higher importance of the ABMs, which
are indeed at the heart of the 1149.4 standard. These 20 switching patterns are
presented in table 1, together with a short description of their corresponding
operating modes.
Pattern
|
Switch conditions
|
Pin
state
|
SD
|
SH
|
SL
|
SG
|
SB1
|
SB2
|
P0
|
0
|
0
|
0
|
0
|
0
|
0
|
Completely isolated (CD
state).
|
P1
|
0
|
0
|
0
|
0
|
0
|
1
|
Monitored by AB2.
|
P2
|
0
|
0
|
0
|
0
|
1
|
0
|
Connected to AB1.
|
P3
|
0
|
0
|
0
|
0
|
1
|
1
|
Connected to AB1; monitored by AB2.
|
P4
|
0
|
0
|
0
|
1
|
0
|
0
|
Connected to VG.
|
P5
|
0
|
0
|
0
|
1
|
0
|
1
|
Connected to VG; monitored by AB2.
|
P6
|
0
|
0
|
0
|
1
|
1
|
0
|
Connected to VG and AB1.
|
P7
|
0
|
0
|
0
|
1
|
1
|
1
|
Connected to VG and AB1; monitored
by AB2.
|
P8
|
0
|
0
|
1
|
0
|
0
|
0
|
Connected to VL.
|
P9
|
0
|
0
|
1
|
0
|
0
|
1
|
Connected to VL; monitored by AB2.
|
P10
|
0
|
0
|
1
|
0
|
1
|
0
|
Connected to VL and AB1.
|
P11
|
0
|
0
|
1
|
0
|
1
|
1
|
Connected to VL and AB1; monitored
by AB2.
|
P12
|
0
|
1
|
0
|
0
|
0
|
0
|
Connected to VH.
|
P13
|
0
|
1
|
0
|
0
|
0
|
1
|
Connected to VH; monitored by AB2.
|
P14
|
0
|
1
|
0
|
0
|
1
|
0
|
Connected to VH and AB1.
|
P15
|
0
|
1
|
0
|
0
|
1
|
1
|
Connected to VH and AB1; monitored
by AB2.
|
P16
|
1
|
0
|
0
|
0
|
0
|
0
|
Connected to core; isolated from all test
circuits.
|
P17
|
1
|
0
|
0
|
0
|
0
|
1
|
Connected to core;
monitored by AB2.
|
P18
|
1
|
0
|
0
|
0
|
1
|
0
|
Connected to core and AB1.
|
P19
|
1
|
0
|
0
|
0
|
1
|
1
|
Connected to core and AB1; monitored by AB2.
|
Table 1:
ABMs – Switching structure patterns.
Switching patterns P1
to P5, which refer to controllability and observability operations where the
core is disconnected from the pin, represent the main testing conditions for
analog measurements. An example of such operations is shown in figure 1, which
illustrates the effect of switching pattern P3.
Figure 1:
Switching pattern P3 (simultaneous controllability and observability).
The normal mission
mode corresponds to switching pattern P16, illustrated in figure 2.
Figure 2:
Switching pattern P16 (normal mission mode).
Similarly to what was
seen before concerning the TBIC switching structure, the selection of each
switching pattern is again a function of the 4-bit code shifted into the ABMs
control structure and of the current instruction, as described in table 2.
Code
C
/ D / B1 / B2
|
Instruction
|
Code
C / D / B1 / B2
|
Instruction
|
EXTEST,
CLAMP
|
PROBE,
INTEST
|
EXTEST,
CLAMP
|
PROBE,
INTEST
|
0000
|
P0
|
P16
|
1000
|
P8
|
*
|
0001
|
P1
|
P17
|
1001
|
P9
|
*
|
0010
|
P2
|
P18
|
1010
|
P10
|
*
|
0011
|
P3
|
P19
|
1011
|
P11
|
*
|
0100
|
P4
|
*
|
1100
|
P12
|
*
|
0101
|
P5
|
*
|
1101
|
P13
|
*
|
0110
|
P6
|
*
|
1110
|
P14
|
*
|
0111
|
P7
|
*
|
1111
|
P15
|
*
|
Table 2:
ABMs – Switching pattern requirements.
(an asterisk
indicates a code word / instruction for which the current version of the
standard does not define any specific operating mode)
Notice that the same
4-bit code may in fact select different operating modes, according to the
contents of the instruction register. As an example, figure 3 shows the
operating modes defined by the 4-bit code word 0011, when the current
instruction is EXTEST / CLAMP (a) or PROBE / INTEST (b).
(a)
EXTEST / CLAMP.
(b) PROBE / INTEST.
Figure 3:
Operating modes defined for code word 0011.
|