Up/down counting

An entry sensor adds 1 and an exit sensor takes 1 away, so ACC is the number of parts in the buffer.

Step by step

Pick a step. The rungs are drawn by the editor after Core scans the program up to that step.

Global.InEye

Global.Buffer

PRE 2 ACC 1 CU 1 CD 0 DN 0 OV 0 UN 0

Global.OutEye

Global.Buffer

PRE 2 ACC 1 CU 1 CD 0 DN 0 OV 0 UN 0

Global.Buffer.DN

Global.BufferFull

1. Part in. The CTU adds 1. ACC is 1.

Step	InEye	OutEye	Buffer.ACC	BufferFull
1. Part in	1	0	1	0
2. Gap	0	0	1	0
3. Part in	1	0	2	1
4. Part out	0	1	1	0
5. Gap	0	0	1	0

CTU and CTD name the same COUNTER tag, so they share one ACC.
Each counts only when its own rung turns on, so a part held in front of a sensor counts once.
DN is on while ACC is at or above PRE, here when the buffer holds 2 parts.

Two counter tagsA CTU on one tag and a CTD on another cannot share a total. Use one tag for both.