AN 100: In-System Programmability Guidelines

ID 683546
Date 9/22/2014
Document Table of Contents

1.1.5. I/O Pins Tri-Stated During In-System Programming

By default, all device I/O pins are tri-stated during in-system programming. In addition, MAX devices provide a weak pull-up resistor during ISP. The purpose of this weak pull-up resistor is to eliminate the requirement for external pull-up resistors on tri-stated I/O pins.

You must add sufficient pull-up or pull-down resistors on signals that require a particular value during in-system programming (for example, JTAG configuration signals). If a pull-up or pull-down resistor is not added, the device could have high current during in-system programming (caused by conflicts on the board), in-system programming failures with either unrecognized device or verify errors, or a power up after in-system programming fails.

For MAX II, MAX V and MAX 10 devices, you can use the in-system programming clamp feature or the real-time ISP feature to ensure that each I/O pin is clamped to a specific state during in-system programming.