Overflow and underflow of the counter limits

Counter overflow and Counter underflow

An overflow or underflow of the counter limits is indicated by the process data 0x6000:04 "Counter underflow" or 0x6000:05 "Counter overflow".

• The "Counter underflow" bit in index 0x6000:04 is set when an underflow 0x8001:1B "Reset counter value" → 0x8001:1A "Limit counter value" occurs.
• With the preset parameters, this corresponds to "..00 → ..FF"
  It is reset if 2/3 of the counter range are underrun.
• For counter limits with fixed value range, this corresponds to:
  2/3 * ("Limit counter value" - "Reset counter value") + "Reset counter value"
• The "Counter overflow" bit 0x6000:05 is set when an overflow 0x8001:1A "Limit counter value" → 0x8001:1B "Reset counter value" occurs.
• With default parameters "..FF → ..00"
  It is reset if 1/3 of the counter range is exceeded.
• For counter limits with fixed value range, this corresponds to:
  1/3 * ("Limit counter value" - "Reset counter value") + "Reset counter value"

Example 1:

0x8001:1A "Limit counter value" = 2¹²-1 = 4095

0x8001:1B "Reset counter value" = 0

"Counter underflow" bit is reset when: 2/3 * 4095 = 2730 is reached.

"Counter overflow" bit is reset when: 1/3 * 4095 = 1365 is reached.

Example 2:

0x8001:1A "Limit counter value" = 2¹²-1 = 4095

0x8001:1B "Reset counter value" = 400

"Counter underflow" bit is reset when: 2/3 * (4095-400) +400 = 2463 is reached.

"Counter overflow" bit is reset when: 1/3 * (4095-95) +400 = 1232 is reached.