Apparatus for testing a phrase-locked loop in a boundary scan enabled device
View Patent ↗An apparatus for interfacing a phase locked loop in a field programmable gate array. The apparatus comprising a phase locked loop cluster. The phase locked loop further comprising a plurality of RT modules, a plurality of RO modules, at least one TY module, a plurality of receiver modules and at least one buffer module. A phase locked loop selectively coupled to the RT modules, the RO modules, the TY modules, the receiver modules and at least one buffer module in the phase locked loop cluster.
1. Apparatus in an integrated circuit, comprising:
a first I/O pad;
a second I/O pad;
a first boundary scan register coupled to the first I/O pad;
a second boundary scan register coupled to the second I/O pad, the boundary scan register including a control bit position;
a phase locked loop test register for storing phase locked loop test control data and coupled between the first boundary scan register and the second boundary scan register;
a phase locked loop;
a phase locked loop cluster for storing phase locked loop operating control data; and
a multiplexer having a first set of data inputs coupled to the phase locked loop cluster, a second set of data inputs coupled to the phase locked loop test register, a set of outputs coupled to the phase locked loop and a control input coupled to the control bit position in the boundary scan register.
2. The apparatus of claim 1 wherein the phase locked loop test register further includes:
a serial chain of bit stages, a first bit stage having an input coupled to the first boundary scan register, a last bit stage having an output coupled to the second boundary scan register, and a plurality of intermediate bit stages coupled between an output of the first bit stage and an input of the last bit stage;
a multiplexer having a first data input coupled to the input of the first bit stage, a second data input coupled to the output of the last bit stage, and a select input coupled to a TEST_PLL signal.
3. The apparatus of claim 2 wherein the first bit stage of the phase locked loop test register includes:
an input node;
an output node;
a bit-stage input multiplexer including a first data input coupled to the input node, a second data input, a control input, and an output;
a first flip-flop having a data input coupled to the output of the bit-stage input multiplexer, a Q output coupled to the output node, and a clock input; and
a second flip-flop having a data input coupled to the output of the first flip-flop, a Q output, a clock input, and a clear input.
4. The apparatus of claim 3 wherein each intermediate bit stage and the last bit stage include:
an input node coupled to the output node of an immediately-preceding bit stage;
an output node;
a bit-stage input multiplexer including a first data input coupled to the input node, a second data input, a control input, and an output;
a first flip-flop having a data input coupled to the output of the bit-stage input multiplexer, a Q output coupled to the output node, and a clock input; and
a second flip-flop having a data input coupled to the output of the first flip-flop, a Q output, a clock input, and a clear input; and
a bit-stage output multiplexer having a first data input coupled to the Q output of the second flip-flop, a second data input coupled to a control bit input node, a select input coupled to the Q output of the second flip-flop of the first bit stage, and an output coupled to a control bit output node.