a semiconductor substrate comprising a plurality of modules, the plurality of modules comprising a first subset of modules and a second subset of modules, wherein the first subset of modules is mutually exclusive of the second subset of modules;

the first subset of modules testable by a first scan chain, and including a first non-volatile memory, the first scan chain comprising a first input to receive a first scan data for the first subset of modules, a second input to receive a first signal to shift data at the first input through the first scan chain, and a first output to provide second scan data from the first scan chain;

the second subset of modules testable by a second scan chain, the second scan chain comprising a first input to receive a third scan data for the second subset of modules, a second input to receive a second signal to shift data at the first input through the second scan chain, and a first output to provide a fourth scan data from the second scan chain;

a scan chain enable module comprising a first input coupled to a bond pad of the semiconductor substrate to receive a select indicator, a second input coupled to receive a third signal to shift scan data, a third input to receive scan-in data to test at least the second subset of modules, a fourth input coupled to the first output of the first subset of modules, a first output coupled to the first input of the first subset of modules to provide a representation of the scan-in data in response to the select indicator having a first value, a second output coupled to the first input of the second subset of modules to provide a representation of the scan-in data in response to the select indicator having a second value, and to provide a representation of the second scan data from the first scan chain in response to the select indicator having the first value;

the scan chain enable module further comprising a shift enable module comprising a first input coupled to the first input of the scan chain enable module, a second input coupled to the second input of the scan chain enable module, and an output coupled to the second input of the first subset of modules to provide the first signal, the shift enable module to provide a representation of a signal received at its second input to its output in response to the select indicator having the first value and to refrain from providing the representation of the signal received at its second input to its output in response to the select indicator having the second value; and

a second non-volatile memory and a first field to store a field value, wherein, in response to the first field having a first field value, the second non-volatile memory can be written to, and in response to the first field having a second, field value, the second non-volatile memory is read-only.