Datasheet

SN54LVT8996, SN74LVT8996
3.3-V 10-BIT ADDRESSABLE SCAN PORTS
MULTIDROP-ADDRESSABLE IEEE STD 1149.1 (JTAG) TAP TRANSCEIVERS
SCBS686A – APRIL 1997 – REVISED DECEMBER 1999
13
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
address matching
Connect status of the ASP is computed by a match of the address received in the last valid shadow protocol
against that at the address inputs (A9–A0) as well as against the three dedicated addresses that are internal
to the ASP (DSA, RSA, and TSA). The address map is shown in Table 2.
Table 2. Address Map
ADDRESS NAME
BINARY
CODE
HEX
CODE
SHADOW-PROTOCOL
RESULT
RESULTANT
PRIMARY-TO-SECONDARY
CONNECT STATUS
Reset Address (RSA) 0000000000 000 RESET RESET
Matching Address A9–A0 A9–A0 MATCH ON
Disconnect Address (DSA) 1111111110 3FE DISCONNECT OFF
Test Synchronization Address (TSA) 1111111111 3FF TEST SYNCHRONIZATION MULTICAST
All Other Addresses All others All others NO MATCH OFF
If the shadow-protocol address matches the address inputs (A9–A0), then the ASP responds by transmitting
an acknowledge protocol. Following the complete transmission of the acknowledge protocol, the ASP assumes
ON status (in which PTDI, PTDO, and PTMS are connected to STDO, STDI, and STMS, respectively). The ON
status allows the scan chain associated with the ASP’s secondary TAP to be controlled from the multidrop
primary TAP as if it were directly wired as such. Figures 6 and 7 show the shadow-protocol timing for MATCH
result when the prior ASP connect status is ON and OFF, respectively.
If the shadow-protocol address does not match the address inputs (A9–A0), then (unless the address is one
of the three dedicated global addresses described below) the ASP responds immediately by assuming the OFF
status (in which PTDO and STDO are high impedance and STMS is held at its last level). This has the effect
of deselecting the scan chain associated with the ASP secondary TAP, but leaves the TAP state of the scan chain
unchanged. No acknowledge protocol is sent. Figures 8 and 9 show the shadow-protocol timing for NO MATCH
result when the prior ASP connect status is ON and OFF, respectively.
disconnect address
The disconnect address (DSA) is one of the three internally dedicated addresses that are recognized globally.
When an ASP receives the DSA, it immediately responds by assuming the OFF status (in which PTDO and
STDO are high impedance and STMS is held at its last level). This has the effect of deselecting the scan chain
associated with the ASP secondary TAP, but leaves the TAP state of the scan chain unchanged. No
acknowledge protocol is sent. Figures 10 and 11 show the shadow-protocol timing for DISCONNECT result
when the prior ASP connect status is ON and OFF, respectively.
The same result occurs when a nonmatching address is received. No specific action to disconnect an ASP is
required, as a given ASP is disconnected by the address that connects another. The dedicated DSA ensures
that at least one address is available for the purpose of disconnecting all receiving ASPs. It is especially useful
when the currently selected scan chain is in a different TAP state than that to be selected. In such a case, the
DSA is used to leave the former scan chain in the proper state, after which the primary TAP state is moved to
that needed to select the latter scan chain.
reset address
The reset address (RSA) is one of the three internally dedicated addresses that are recognized globally. When
an ASP receives the RSA, it immediately responds by assuming the RESET status (in which PTDO and STDO
are high impedance and STMS is forced to the high level). This has the effect of deselecting and resetting (to
Test-Logic-Reset state) the scan chain associated with the ASP secondary TAP. No acknowledge protocol is
sent. Figures 12 and 13 show the shadow-protocol timing for RESET result when the prior ASP connect status
is ON and OFF, respectively.