GS4901B/GS4900B Preliminary Data Sheet
3.11 JTAG
When the JTAG/HOST input pin of the GS4901B/GS4900B is set HIGH, the host
interface port will be configured for JTAG test operation. In this mode, pins 57
through 60 become TCLK, TDI, TDO, and TMS. In addition, the RESET pin will
operate as the test reset pin.
Boundary scan testing using the JTAG interface will be enabled in this mode.
There are two methods in which JTAG can be used on the GS4901B/GS4900B:
1. As a stand-alone JTAG interface to be used at in-circuit ATE (Automatic Test
Equipment) during PCB assembly; or
2. Under control of the host for applications such as system power on self tests.
When the JTAG tests are applied by ATE, care must be taken to disable any other
devices driving the digital I/O pins. If the tests are to be applied only at ATE, this
can be accomplished with high-impedance buffers used in conjunction with the
JTAG/HOST input signal. This is shown in
Application HOST
GS4911B/GS4910B
CS_TMS
SCLK_TCLK
SDIN_TDI
SDOUT_TDO
JTAG/HOST
In-circuit ATE probe
Figure 3-16: In-Circuit JTAG
Alternatively, if the test capabilities are to be used in the system, the host may still
control the JTAG/HOST input signal, but some means for tri-stating the host must
exist in order to use the interface at ATE. This is represented in
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