Texas Instruments 990 User Manual page 99

Applications Programming
4.3 PROGRAMMING EXAMPLES AND APPLICATIONS NOTES
The following example illustrates how two applications programs
communicate with each other using the communications SVCs.
Figure 4-3 illustrates· the flow of data between applications
programs in a primary station and a secondary station when using
the conununications package. Applications program B executes in
the secondary station, while applications program A executes in
the primary station. The communications between the two programs
are outlined in steps 1 through 16 as follows:
1. Applications program B is activated in the secondary
station at warm start.
2. Program B requests activation from suspension by
calling activation services with an I/O opcode 4.
3. Program B executes a call to the operating system for
indefinite suspension. (Activation services begins
searching the communications input buffers for data
addressed to program B.)
4. Applications program A at the primary station is
activated.
5. Program A processes and prepares
subsequent use by program B.
the data for
6. Program A executes a call to write/send data to program
B with an I/O opcode 2.
7. Program A requests activation from a time delay by
calling activation services with an I/O opcode 5.
8. Program A executes a call to the operating system for a
20-second time delay. (Activation services begins
searching the communications input buffers for data
addressed to program A.)
9. When the data addressed to program
sec onda ry sta tion, ac t iva t ion
program B.
B arrives at the
services activates
10. Program B executes a call to read the input data
addressed to it with an I/O opcode 3.
11. Program B processes the data it receives and prepares
to send a response to program A acknowledging the
receipt of da ta.
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