Toshiba T2N - Manual (Page 119)

2.INTERNAL OPERATIONS
106 PROSEC T2N
†, Š Batch I/O processing
The data exchange between the I/O image table (I/O register/device) and
the I/O module is performed on the basis of the I/O allocation information.
Data exchange with the data transmission module (TOSLINE-S20LP,
TOSLINE-F10, TOSLINE-30) also takes place. The first scan is input only.
Batch I/O processing is explained in 2.4.2.
‡, Timer update
The timer register using the timer instruction is updated and the special
relay timing relay (S0040 - S0047) is updated.
Timer update is explained in 2.4.3.
ˆ, Running user program
The user program instructions are executed in sequence from the
beginning to the END instruction. Here, the user program consists of a
main program and sub program.
When the interrupt conditions are set up, interrupt programs halt other
operations and are activated immediately.
The user program running control is explained in detail in section 3.
‰ Mode control
Checks the mode switch and for mode change commands from the
programmer and changes operation mode. Also, scan timing control,
measurement of the scan cycle and the user program running time are
performed.
In the T2N the scan mode enables a choice of floating scan and constant scan.
The floating scan mode is that, immediately after one scan is complete the next
scan commences. It is the shortest scan cycle but the scan cycle varies
according to the user program running state.
The action of the floating scan is shown in the following diagram.
2.4.1
Scan mode
scan cycle
mode I/O Timer User program Mode I/O Timer User program
scan cycle
next scan begins mmediately