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SN74ABT8996PW Folha de dados(PDF) 6 Page - Texas Instruments |
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SN74ABT8996PW Folha de dados(HTML) 6 Page - Texas Instruments |
6 / 46 page SN54ABT8996, SN74ABT8996 10-BIT ADDRESSABLE SCAN PORTS MULTIDROP-ADDRESSABLE IEEE STD 1149.1 (JTAG) TAP TRANSCEIVERS SCBS489C – AUGUST 1994 – REVISED APRIL 1999 6 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 architecture Conceptually, the ASP can be viewed as a bank of switches that can connect or isolate a module-level TAP to/from a higher-level (e.g., module-to-module) TAP. This is shown in Figure 2. The state of the switches (open versus closed) is based on shadow protocols, which are received on PTDI and are synchronous to PTCK. The simple architecture of the ASP allows the system designer to overcome the limitations of IEEE Std 1149.1 ring and star configurations. Ring configurations (in which each module’s TDO is chained to the next module’s TDI) are of limited use in backplane environments, since removal of a module breaks the scan chain and prevents test of the remainder of the system. Star configurations (in which all module TDOs and TDIs are connected in parallel) are suited to the backplane environment, but, since each module must receive its own TMS, are costly in terms of backplane routing channels. By comparison, use of the ASP allows all five IEEE Std 1149.1 signals to be routed in multidrop fashion. 1 0 Control CON STDI STCK STMS STDO STRST PTDO PTCK PTMS PTDI PTRST BYP A9–A0 From Multidrop, Module-to-Module Test Access Port To Module-Level Test Access Port Figure 2. ASP Conceptual Model As shown in the functional block diagram, the ASP comprises three major logic blocks. Blocks for shadow-protocol receive and shadow-protocol transmit are responsible for receipt of select protocol and transmission of acknowledge protocol, respectively. The connect-control block is responsible for TAP-state monitor and address matching. Some additional logic is illustrated outside of these major blocks. This additional logic is responsible for controlling the activity of the ASP outputs based on the shadow-protocol result and/or protocol bypass [as selected by an active (low) BYP input]. |
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