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SN74LVT8980DW Datasheet(PDF) 6 Page - Texas Instruments |
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SN74LVT8980DW Datasheet(HTML) 6 Page - Texas Instruments |
6 / 37 page SN54LVT8980, SN74LVT8980 EMBEDDED TEST BUS CONTROLLERS IEEE STD 1149.1 (JTAG) TAP MASTERS WITH 8BIT GENERIC HOST INTERFACES SCBS676E − DECEMBER 1996 − REVISED MARCH 2004 6 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 application information (continued) The eTBC also provides several capabilities that support special target application requirements. The eTBC’s test-output enable allows its master function to be disabled so that another device (an external tester, for example) can control the target TAP. Where required, due to target noncompliance or sensitivity to state sequencing, discrete-control mode provides the host software with arbitrary control of TMS and TDO sequences. Also, where targets may be sensitive to leaving Shift-DR state during scan operation, gated-TCK mode allows the TCK output to be stopped, rather than cycling the target TAP state to Pause-DR state, when service to TDI buffer or TDO buffer is required. Where target devices are extremely distant (due to cabling, etc.), pipelining may be implemented at intervals along the incoming or outgoing paths to retime (deskew) the TDI, TDO, and TMS signals. An example is shown in Figure 2. In such applications, the eTBC automatically can adjust the incoming test-data bit stream to account for cycle delays introduced by the pipeline. TDI TDO TMS TCK ’LVT8980 eTBC 1D 1D 1D C1 Distant IEEE Std 1149.1- Compliant Device Chain Figure 2. Retimed Interface to Target Also, in gated-TCK mode, special scan commands provide transparent support for addressable shadow protocols. Thus, in conjunction with its high-drive outputs, the eTBC can fully support multidrop backplane TAP configurations implemented with TI’s addressable scan ports (ASP). Figure 3 shows a multidrop TAP configuration in a passive-backplane application implemented with a centralized (one eTBC per chassis/rack) test-control architecture, while Figure 4 shows a passive-backplane application implemented with a distributed (eTBC per module) test-control architecture. Figure 5 shows a multidrop TAP configuration in an active-backplane (motherboard) application. |
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