IEC运算符减去变量。
允许的数据类型：BYTE, WORD, DWORD, LWORD, SINT, USINT, INT, UINT, DINT, UDINT, LINT, ULINT, REAL, LREAL, TIME, LTIME, TIME_OF_DAY (TOD), LTIME_OF_DAY (LTOD), DATE, LDATE, DATE_AND_TIME (DT) LDATE_AND_TIME (DT)
.时间数据类型的可能组合：
- TIME - TIME = TIME
- LTIME - LTIME = LTIME
.日期和时间数据类型的可能组合：
- DATE - DATE = TIME
- LDATE - LDATE = LTIME
- TOD - TIME = TOD
- LTOD - LTIME = LTOD
- TOD - TOD = TIME
- LTOD - LTOD = LTIME
- DT - TIME = DT
- LDT - LTIME = LDT
- DT - DT = TIME
- LDT - LDT = LTIME
 | TIME/LTIME负值无定义。 |
