In order to interface an 8051 to an asynchronous peripheral chip, I am looking for an 8051 variant that has the ability to access xdata memory asynchronously. In other words, I need an 8051 that can wait for an external hardware signal before latching xdata from the data bus (I'm not talking about programmable wait states, which are available on chips such as the DS80C320).

I know that Mentor Graphics makes an FPGA processor core that has this asynchronous bus feature, but I am looking for a manufactured chip at this point.

Can anyone point me to such a device? Thank you.