What is the parameter tRV found in the data sheet timing diagrams?
A12. The parameter tRV is not found in the 82C55A or 8255A wave forms. However, it is the time between reads and writes, as stated in the 8255A data sheet. Q13. Is a customer able to drop an 82C55A device into the NMOS 8255A socket? Should a customer be concerned about the ability of the chip to drive a Darlington pair? A13. All three ports of the 82C55A can source 2.5mA and drive Darlington pairs. The user must limit the current the chip sinks to the data sheet limits. The 82C55A still requires external pull-ups. The internal pull-ups designed to terminate the unused port pins in the 82C55A function if the pins are loaded with less than 20pF. Loads greater than 20pF will not have the logic level guaranteed by the internal pull-ups. Refer to the tech bit covering the port hold device description. Q14. What are the two data sheet parameters IPHLO and IPHHO (Port Hold Low/High Overdrive Current)? A14. There is a 4-page tech-bit called Reading from Output Ports and another called Port Hol
