Test interface with access across isolation barrier

1. A method comprising:

receiving first diagnostic data at a transmit die;

transmitting the first diagnostic data over an isolation channel to a receive die;

receiving the first diagnostic data at the receive die;

supplying a signal from an internal node in the receive die to an output terminal of the receive die, the internal node in the receive die identified by the first diagnostic data;

selecting one of a first plurality of blocks in the receive die based on a block select portion of the first diagnostic data; and

selecting one of a first plurality of nodes within the one of the first plurality of blocks as the internal node.

2. The method as recited in claim 1 wherein the transmit die and receive die are disposed in a package.

3. The method as recited in claim 1 , further comprising supplying one of an analog signal and a digital signal from the one of the first plurality of nodes.

4. The method as recited in claim 1 , further comprising:

receiving second diagnostic data at the transmit die; and

supplying a second signal from an internal node in the transmit die to an output terminal of the transmit die, the internal node in the transmit die identified by the second diagnostic data.

5. The method as recited in claim 4 , further comprising:

selecting one of a second plurality of blocks in the transmit die with a block select portion of the second diagnostic data; and

selecting one of a second plurality of nodes within the one of the second plurality of blocks as the internal node in the transmit die.

6. The method as recited in claim 1 , further comprising:

receiving second data at the transmit die;

sending the second data from the transmit die to the receive die over the isolation channel;

configuring a first analog block in the receive die based on the second data;

receiving third data at the transmit die;

sending the third data to the receive die; and

supplying a second signal from a second internal node in the receive die to the output terminal of the receive die while the first analog block remains configured according to the second data, the second internal node in the receive die identified by the third data.

7. A method comprising:

receiving first diagnostic data at a transmit die;

transmitting the first diagnostic data over an isolation channel to a receive die;

receiving the first diagnostic data at the receive die;

supplying a signal from an internal node in the receive die to an output terminal of the receive die, the internal node in the receive die identified by the first diagnostic data;

receiving second diagnostic data at the receive die from the transmit die prior to receiving the first diagnostic data while a voltage being supplied to the receive die is below a full operational voltage; and

unlocking a diagnostic mode in the receive die based on the second diagnostic data thereby allowing the first diagnostic data to cause the signal from the internal node in the receive die to be supplied to the output terminal of the receive die.

8. An apparatus:

a transmit die coupled to an isolation channel and configured to transmit first diagnostic data received over an isolation channel to a receive die;

receive logic in the receive die coupled to the isolation channel and configured to select an internal node in the receive die based on the first diagnostic data;

an output terminal on the receive die coupled to receive a signal from the internal node, the signal indicating a state of the internal node; and

wherein the first diagnostic data includes block select information to select one of a plurality of blocks within the receive die and the first diagnostic data includes node select information to select one of a plurality of nodes within the one of the plurality of blocks as the internal node.

9. The apparatus as recited in claim 8 wherein the transmit die and receive die are disposed in a package.

10. The apparatus as recited in claim 8 , wherein the signal from the internal node is one of an analog signal and a digital signal.

11. The apparatus as recited in claim 8 , further comprising:

second receive logic in the transmit die coupled to receive second data from an input terminal of the transmit die and configured to supply select signals to select a transmit die node; and

an output terminal in the transmit die coupled to the transmit die node to supply a second signal received therefrom.

12. The apparatus as recited in claim 8 ,

wherein the receive logic is further configured to configure a first analog block in the receive die according to second data received over the isolation channel and to select a second internal node in a second analog block of the receive die to be coupled to the output terminal of the receive die while the first analog block remains configured according to the second data, the second internal node in the receive die identified by third data received over the isolation channel.

13. The apparatus as recited in claim 12 ,

wherein at least one of a voltage or a current setting in the first analog block is configured based on the second data.

14. The apparatus as recited in claim 8 , wherein the block select information provides block select signals and only one of the block select signals is in an asserted state at a time.

15. An apparatus comprising:

a transmit die coupled to an isolation channel and configured to transmit first diagnostic data received over an isolation channel to a receive die;

receive logic in the receive die coupled to the isolation channel and configured to select an internal node in the receive die based on the first diagnostic data; and

an output terminal on the receive die coupled to receive a signal from the internal node, the signal indicating a state of the internal node; and

wherein the receive logic is configured to require one or more second diagnostic data be written to one or more addresses in the receive logic to unlock diagnostic functionality of the receive die prior to the first diagnostic data being written to the receive die to probe the receive die, the second diagnostic data being written while voltage being supplied to the receive die is below an operational level.

16. An apparatus comprising:

an isolation channel;

a transmit die having an input terminal to receive first diagnostic data and configured to transmit the first diagnostic data over the isolation channel;

a receive die coupled to receive the first diagnostic data over the isolation channel, the first diagnostic data including one or more unlock codes for writing to one or more addresses in the receive die to enable receive die diagnostic capability if the one or more unlock codes are supplied while a receive die voltage supply is at a first voltage level and the receive die diagnostic capability is disabled if the receive die voltage supply reaches a second voltage level before the one or more unlock codes are supplied;

wherein the receive die is responsive to second diagnostic data received after the receive die diagnostic capability is enabled to select an internal node; and

wherein the receive die is responsive to the second diagnostic data to couple the internal node to an output terminal of the receive die if the receive die diagnostic capability is enabled.

17. The apparatus as recited in claim 16 further comprising:

a level detect circuit to detect a voltage level of the receive die voltage supply and to supply an indication of whether the receive die voltage supply is at the first voltage level or the second voltage level.

18. The apparatus as recited in claim 17 wherein the second voltage level is an operational voltage level for the receive die and is higher than the first voltage level.