Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)1 J. M. Martins Ferreira FEUP / DEEC - Rua Dr. Roberto Frias Porto - PORTUGAL Tel / Fax: / Overview of the IEEE 1149.x test standards Design for Test Seminar

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)2 Boundary-scan (1149.1) Mixed-signal (1149.4) AC testing (1149.6) Why and where to use? The BS test principle Test access port and BS architecture BS instructions

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)3 Why Boundary Scan Test? The two main reasons that led in the mid- 80s to the development of BST were: –The complexity of ICs made it exceedingly difficult to develop test programs for the functional test of complex PCBs –Small outline surface mount devices and advanced mounting technologies almost disabled physical access to internal PCB nodes and made in-circuit test exceedingly difficult

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)4 The application domain of BST BST addresses the structural test of digital printed circuit boards Keywords: structural, digital, PCBs This embedded test infrastructure is now used for other purposes as well (e.g. in-system programming)

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)5 The BS test principle BS uses a Test Access Port (TAP) to decouple the internal IC logic from the pins and allows “direct” access to any PCB node without backdriving effects

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)6 The BS architecture Main blocks: –BST register –BP register –Instruction register –TAP controller –Other registers

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)7 The basic BS cell Three modes of operation: –Transparency –Controllability –Observability

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)8 TAP controller state transition diagram

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)9 BST instructions Mandatory: –EXTEST –SAMPLE / PRELOAD –BYPASS Optional: –INTEST, RUNBIST, CLAMP, IDCODE, USERCODE, HIGHZ

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)10 Boundary-scan (1149.1) Mixed-signal (1149.4) AC testing (1149.6) : an extension of TBIC and ABMs (internal test circuitry) The PROBE instruction Parametric testing

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)11 The std defines an extension to , to which it adds: –An analog test port (ATAP) with two pins (AT1, AT2) –An internal analog test bus (AB1, AB2) –A test bus interface circuit (TBIC) –The analog boundary modules (ABM) The IEEE standard for mixed signal test

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)12 The test bus interface circuit (TBIC) The TBIC defines the interconnections between the ATAP (AT1 and AT2) and the internal analog test bus (at least two lines, AB1 and AB2) The TBIC comprises a switching structure and a control structure

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)13 TBIC: The switching structure

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)14 TBIC: Control structure

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)15 The analog boundary modules (ABM) The ABMs in the analog pins extend the test functions made available by the DBMs All test operations combine digital (via TAP) and analog test “vectors” (via ATAP) Each ABM comprises a switching structure and a control structure

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)16 ABMs: Switching structure

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)17 ABMs: Control structure

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)18 The register structure The register structure is entirely digital and identical to the corresponding structure

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)19 The PROBE instruction The IEEE std defines a fourth mandatory instruction called PROBE: –The selected data register is the BS register –One or both of the ATAP pins connect to the corresponding AB1/AB2 internal test bus lines –Analog pins connect to the core and to AB1/AB2 as defined by the ABM 4-bit control word –Each DBM operates in transparent mode

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)20 Impedance measurement between pin and ground ITIT V VTVT Z D = V T / I T if: Z V >> Z S6 + Z SB2 Z V + Z S6 + Z SB2 >> Z D ZDZD

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)21 Boundary-scan (1149.1) Mixed-signal (1149.4) AC testing (1149.6) Scope and objectives Test of AC-coupled differential networks test cells and instructions

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)22 Scope and objectives Scope of : Structural test of high- speed digital networks Objectives –Cope with differential and/or AC-coupled interconnections, enabling high fault coverage with minimum impact on mission logic –Reuse as much as possible IEEE tools (ensure compatibility with / 4)

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)23 AC-coupling, differential signalling Single-ended signalling with AC-coupling Differential signalling with AC-coupling and bias provision TX: RX:

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC)24 Testing AC-coupled / differential networks BS cell placement has an impact on circuit performance and defect coverage Modified BS cells must ensure: –Signal transmission over AC-coupled nets –Logic level detection from AC test signals

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC) test cells An AC testing instruction selects the AC Mode, and a test signal suited for AC-coupled networks is applied to the pin A test receiver at the input cell derives logic level information from the incoming AC / DC test signal (valid transitions)

Design for Test HIBU – Oct. 31st 2006 J. M. Martins Ferreira - University of Porto (FEUP / DEEC) instructions EXTEST_PULSE generates a transition even when the new test value at the driver pin retains its previous value EXTEST_TRAIN provides multiple additional transitions (to cope with transient conditions, when necessary) Both cause the driver pins to change state at least twice in Run-Test / Idle (from a Geek Squad add) Coffee break