RTC
®
4 PC Interface Board
Rev. 1.3 e
4 Principle Of Operation
13
innovators for industry
List Handling
The command set_start_list (see page 116) opens a
list buffer for writing. After finishing the data input,
the list must be closed with the command
set_end_of_list.
As soon as a list is closed, it can be started either with
the command execute_list (see page 81) or by an
external start signal (see the section "External Control
Inputs", right).
During the execution of one list, the other list buffer
can be loaded with the next list. The host computer
and the RTC
®
4 then work in parallel. The second list
can only be started after execution of the first list has
finished. During execution of a list, execute_list
commands and external start signals are ignored.
Execution of a list can be stopped at any time, e.g. for
implementing an emergency shutdown or for any
other purpose. Use of the stop_execution command
(see page 119) or an external stop signal will imme-
diately abort the currently running list and turn off all
RTC
®
4 laser signals.
To examine the current status of the lists, the
commands get_status (page 86) or read_status
(page 100) can be used.
Automatic List Handling
Continuous Transfer
The commands auto_change and auto_change_pos
(see page 75) activate an automatic list change. That
causes the next sequence of commands to start auto-
matically when the current list is finished. In this
manner, continuous data transfer to the scan head
can be achieved without non-productive pauses.
The command auto_change can be called when
working with two lists (each with a maximum
capacity of 4000 commands). This command should
only be called while a list is executing or after a list
has finished. Additionally, the next list should have
already been loaded and closed (by a call of the
command set_end_of_list).
The auto_change_pos command can be called when
the RTC
®
4’s entire memory is to be treated like a
single list. The start position (address in list memory)
of the next command sequence is specified by the
command.
Repeating Output
Alternatively, continuous data transfer can be
achieved by alternately repeating output of the two
lists:
Load and close the two lists.
Start one of the lists with the command
execute_list.
While the first list is running, call the command
start_loop (see page 119). This causes a
continuous, automatic and alternately repeating
output of both lists from the RTC
®
4 to the scan
head, until you choose to call the command
quit_loop, which will terminate the continuous
output as soon as the current list is finished.
Circular Queue
A completely different mode of operation for
continuous data transfer is described in chapter 5.5
"Circular Queue Mode", page 44.
External Control Inputs
To also enable start and stop execution of a list via
external signals, the RTC
®
4 provides two external
control inputs, /START and /STOP
(TTL active-low). These control inputs are accessible
via the 9-pin D-SUB laser connector VB3 on the RTC
®
4
board – see figure 23 on page 52. Both signal inputs
are internally connected to +5 V via pull-up resistors
(10 kΩ).
Both inputs are active-LOW, i.e. the corresponding
pin must be set to the LOW level (0 V) to start or to
stop execution.
STOP Signal
If the /STOP input is at the LOW level for at least
10 µs, execution of the currently running list is
aborted immediately and the RTC
®
4 laser signals are
turned off. This is equivalent to calling the command
stop_execution (see page 119).
The /STOP input is always enabled. It can, for
instance, be used to implement an emergency
shutdown.
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