Mode 3 (x11): Square Wave Generator:
This mode is alike to mode 2. However, the duration of the low and high clock pulses of the output will be different. Imagine n is the number loaded into the counter (the COUNT message), the output will be following
o High for n/2 counts, and low for n/2 counts, if n is even.
o High for (n+1)/2 counts, and low for (n-1)/2 counts, if n is odd.
Mode 4 (100): Software Triggered Strobe
After COUNT and Control Word are loaded, the output will remain high till the counter reaches zero. Then the counter will generate a low pulse for 1 clock cycle (a strobe) - after that the output will become high again.
Mode 5 (101) : Hardware Triggered Strobe
This mode is alike to mode 4. However, the counting procedure is triggered by the GATE input. After attaining the Control Word and COUNT, the output will be set high. One time the device detects a rising edge on the GATE input, it will begin counting. When the counter attain 0, the output will go low for one clock cycle - after that again it will become high, to repeat the cycle on the next rising edge of GATE.