Function For Accessing Other Stations; Link Data Refresh Time - Hitachi EH-150 Applications Manual

4.3

Function for accessing other stations

It is possible to read, white and control the operations of monitor programs for other stations from peripheral
devices connected to the CPU via the CPU link module.
An example of this is shown in figure 4.6. This enables a peripheral device connected to the EH-150
communication port to operate and monitor a different CPU's program connected to the same link system.
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However, peripheral devices can only access CPUs that are on the same link system (the same loop.)
Note: There are cases where another station's CPU cannot be accessed if an error occurs in the link module
of the station connected to the peripheral device.
4.4

Link data refresh time

The amount of time required for the EH-150 link module to update link data is calculated in the following
manner. However, this is only a rough estimate and does not necessarily apply when transmission errors and
other errors are triggered. As the refresh time is extended in these cases, close consideration must be applied
when designing the system.
Link data refresh time =
Transmission CPU scan time + receiving CPU scan time + A + B x all station's assigned word count + C
x slave station count + 20 (ms) *
* Slave station confirmation time (fixed): The slave station confirmation time is only added to the calculation
if the number of participating units is less that 64.
The A to C values in the above equation are as follows:
(Calculation example)
When ten links exists and each link area is assigned 50 words (scan time for each CPU 20ms, link
transmission speed 1Mbps)
Link data refresh time = 20 + 20 + 25 + (0.04 x 50 x 10) + (3.7 x 9) + 20 = 138ms
ST1
ST2
Figure 4.6 Accessing another station via the link module
Sign Meaning
A Master station processing time
B Processing time / word
C Slave station fixed processing time
Chapter 4. Basic CPU Link Operations
ST3
H-252C
Time (ms)
0.04
4-5
ST0
ST4
H-4010
25
3.7