A transmitter digital signal processor (DSP) circuit has a transmit frequency represented by n-bit data output from a look up table (LUT). The n-bit data is outputted to an n-bit accumulator structured to overflow at a rate based on the output n-bit data to output a phase. The circuit further has device structured to add an n-bit signed constant to the accumulator to offset the frequency represented by the n-bit data output from the LUT. A transceiver on a semiconductor chip may include as part of a transmitter circuit, a transmit DSP circuit that has the LUT, accumulator and device providing an n-bit signed constant to the accumulator to offset a transmit frequency in order to allow a receiver circuit on the transceiver to communicate directly with the transmitter circuit, and thus allowing testing of the transceiver.