[previous] [next] [contents]    The ABM switching structure

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.