Structured Programming; Input Pointer; List Jumps; Conditional List Jumps - Scanlab RTC 4 Installation And Operation Manual

5.6 Structured Programming

The command set of the RTC
list commands for controlling program flow:
• set_list_jump
• list_call
• list_call_cond
• list_jump_cond
• list_return
• list_nop
• These commands use the RTC
a single list buffer with a total capacity of 8000
entries. Each command in the list buffer has a
unique address in the range [0 ... 7999].
Together with the control commands
set_input_pointer and execute_at_pointer, this
allows structured list programming and execution.

Input Pointer

To write a list of commands to a particular location
®
in the RTC 4 list memory, the command
set_input_pointer (see page 106)
(instead of the commands set_start_list_1 /_2).
The command places the input pointer at any address
in the range [0 ... 7999]. The next list command will
be written to this address.
Caution!
• If the end of the list buffer is reached during
writing of a list, the input pointer is reset to
zero, i.e. the next list command is written to the
address zero.
• Make sure not to overwrite any commands
which are still needed by your application.
The current position of the input pointer can be inter-
rogated by calling the command
(see page 83).
®
RTC 4 PC Interface Board
Rev. 1.3 e
5 Advanced Programming
®
4 includes a number of
®
4 list memory as
is used
get_input_pointer

List Jumps

The command set_list_jump (see page 109)
a jump to the specified address. During execution,
®
the RTC 4 jumps to this address.
Similarly, the command list_call
to a subroutine (sub-list). The sub-list has to be
terminated with the command list_return.
The main list must be terminated with the command
set_end_of_list.

Conditional List Jumps

Conditional list jumps and subroutine calls can be
programmed via the commands
list_call_cond: The current value of the 16-bit digital
input port at the EXTENSION 1 connector is read and,
depending on its value, a subroutine is called or a
jump within a list is executed (also see
Examples", page 46 and "16-Bit Digital Input and
Output", page 56).

Output Pointer

To start execution at a particular address, the
command execute_at_pointer (see page 81)
®
be used. The RTC 4 starts execution immediately.
Execution stops when a set_end_of_list
encountered. If the end of the list buffer is reached,
®
the RTC 4 continues at the address zero.
Caution!
• If the end of the list buffer is reached during
execution (and if the last command is not a
set_end_of_list command), execution
continues at the address zero.
If the external start signal (see the section
Control Inputs", page 13) is used, the command
set_extstartpos_list (see page 105)
of the start address for the external list start.
defines
defines a jump
list_jump_cond and
"Programming
must
command is
"External
allows definition
45