Which connection are you using to connect to your board (Multilink, Cyclone Pro, ...)?
With some connections it is possible to disable maskable interrupts while stepping, when checking the "Disable maskable ISR's when stepping" checkbox in "Communication"|"Special Setup" dialog.
Availability of that box depends on the version of the tools you are using and on the connection you are using.
I hope this helps.
Hi thanks for your anwswer,
I use MultilinkBDM to connect to my target board.
Besides, I want to know.
Does the timer of CPU stop counting when MCU halt during the debug? For example: current TCNT: 0x1000, then I press "Single step". ->maybe TCNT become to 0x10FF, and than I press "Single step" again-> myabe TCNT become to 0x11FE. when I don't press any instruction, the TCNT dont change. But Freescale MCU timer can not stop when MCU halt ? Have any method to overcome this problem?