Transponder interface circuit

A transponder interface circuit interposed between a transponder controller and an external interface, said external interface being in electrical communication with circuitry that is external to said transponder, said transponder interface circuit comprising:

• a) an interface controller operable to communicate with said transponder controller;
• b) a buffer memory interposed between said transponder controller and said external interface, said buffer memory in electrical communication with and under control of said interface controller so that said transponder controller can access said buffer memory using a clock signal derived from the transponder clock and so that said external circuitry can access said buffer memory using a clock signal originating in said external circuitry;
• c) a serial I/O buffer between said serial buffer memory and said external interface circuit, said I/O buffer operable to enable communication to or from said buffer memory depending on a control signal from said interface controller;
• d) a clock selection multiplexer for passing a data clocking signal to said buffer memory from one of at least two sources, the first source being said the signal derived from the transponder clock, and the second source being the clock signal originating in said external circuitry, the appropriate source being chosen by a signal to the multiplexer from said interface controller and chosen to correspond with whichever of the transponder and the external circuitry is accessing the buffer memory;
• and
• e) a bit counter in electrical communication with said interface controller and said clock selection multiplexer, said bit counter operable to count the clock transitions of the data clocking signal whereby the interface controller can monitor the progress of the buffer memory access.

A method for communicating between a transponder and circuitry external to said transponder, the method comprising the steps of:

• a) receiving an alert signal from said external circuitry;
• b) loading a buffer memory with read data from another memory within said transponder, said data being clocked into said buffer memory using a clock generated internally to said transponder;
• c) switching the source of the clock signal received by said buffer memory from said internal clock to one originating in said external circuit;
• and
• d) unloading said read data from said buffer memory into an external memory, said read data being clocked out of said buffer memory using said clock signal form said external circuit.

A method for communicating between a transponder and circuitry external to said transponder, the method comprising the steps of:

• a) loading a buffer memory with write data from said external circuitry, said data being clocked into said buffer memory using a clock received form said external circuitry;
• b) switching the source of the clock signal received by said buffer memory from said external clock to one that is generated within said transponder;
• and
• c) unloading said write data from said buffer memory into another memory, said write data being clocked out of said buffer memory using said clock signal that is generated within said transponder.