IBM 1 Series - Page 144

External Sync Mode
The ‘external sync’ line permits the user to control the change of the DO
group. ‘External sync’ meets all of the specifications of a DI point. Figure
5-2 shows the timing for DO external sync.
Program control Program control
- ~~ ~~ rt
Prepare Arm Write DO Service Write DO
| | | |
Ready | | | f. | f.
| | | |
External ! | | | <1 ps | < lus
sync | | |
| | | |
| | | +} | -
Interrupt | |
Figure 5-2. DO external sync timing diagram
This sequence is executed as follows:
1. The external sync mode of operation is initiated by an Arm External
Sync command.
2. The user’s external equipment signifies that it is ready to receive new s,
input from the DO group by activating ‘external sync’ (down level).
3. The system signifies that the Write DO command is complete and that
new data is available by activating the ‘ready’ output (down level).
4. When the external equipment has received the new data, it deactivates
the ‘external sync’ input line (up level).
5. The system then deactivates the ‘ready’ line and posts an interrupt to
the channel, indicating that the external equipment has received the
data.
6. After the interrupt has been serviced, another Write DO command is
performed to set up the group for the next data transfer sequence. The
system is then waiting for the next transition of ‘external sync’ to an
active state.
Diagnostic Mode
The diagnostic mode is entered by performing the Disable DO and the Set
Diagnostic External Sync commands. These instructions disable all outputs
and inputs for the group. If the Set Diagnostic External Sync command is
performed after the Disable DO command, and if the DO group is set up
to perform an external-sync transfer, the Set Diagnostic External Sync
command causes an interrupt to be posted to the channel. If an interrupt is
pending, busy is returned and the commands are not performed. In the
diagnostic mode, all commands and modes operate as usual, except that
the user’s inputs are disabled and the user’s outputs are turned off. When
leaving diagnostic mode, the data in the DO register is placed on the user’s
outputs; the user’s inputs are enabled.
Integrated Digital Input/Output Feature 5-5