On a subtraction, the carry flag becomes a "not borrow" flag. In other words, if the value "passes thru zero" then carry will be clear; otherwise carry will be set. Bob Ammerman RAm Systems ----- Original Message ----- From: "Christopher Gill" To: Sent: Tuesday, November 05, 2002 8:54 AM Subject: [PIC]:Passing through zero I am trying to monitor whether a register value drops below zero when a subtraction is carried out. Is this possible and how? I understand how the carry bit is used to show a register going over 0xFF, I thought the zero bit would have a similar effect in the other direction but this is only set when the value is exactly zero. can anyone help me thanks chris -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.