Remote-processing BASIC 52 Manual do Utilizador descarregar pdf (Página 14)

RPBASIC-52 PROGRAMMING GUIDE

1-11

0 Wait for "RING" message. Modem

auto answers.

1 Look for "CONNE CT".

2 Get password. If invalid, prompt for

password again.

3 Send successful log in message .

Prompt for comm and and process

them.

4 Take modem off line and reset

5 Delay for a few seconds and send sign

on message.

The actual program is more complicated than the

steps indicate. Timeouts are used to disconnect the

modem when there is inactivity. Three failed

passw ord attempts takes t he m odem off line.

Ringing but no connect takes the modem off line.

Superfluous <cr>'s are ignored.

Activity timeout is set for 10 seconds. The

ONTICK routine checks for activity every second

when the program cycle advances to step 1 and

beyond. ON TICK cou ld be faster if it is necessary.

Keep in mind that ONTICK interrupts have the

highest priority. Keep tick interrupt processing

times short and as infrequent as possible. Frequent

and/or long processing times take away from other

program times.

ON COM $ interrupt uses a program cycle pointer

(variable CYCLE) to direct the next activity on an

interrupt. When a message is received, an interrupt

is generated. Processing the message is handled by

the appropriate routine poi nted to by CY CLE . A

<cr><lf> sequence is simply ignored and treated as a

non-event.

After the password is accepted, the main purpose of

the application takes over. There are many

scenarios, or situations, possible:

1. The comp uter is u sed for data log ging.

Dialing in merely dumps data.

2. The computer is used for control. A dial up

is for new instructions or parameters.

3. Some combination of data logging and

control.

4. A computer will dial up and query and/or

issue new instructions.

5. A person using a terminal will dial up the

control card and query and/or issue new

instructions.

6. A computer and/or person at a terminal w ill

dial up and query and/or issue new

instructions.

7. A new program is downloaded to the card.

The number of possible applications is much too

complex to even begin showing code.

Some applications use a person at a term inal to

remotely query the card. In this situation, it is nice

to return a character as soon as it is typed in. This

can be done by setting the users terminal to local

echo. However, you don't know if the card received

what you send. The remote card can echo back

characters as they are sent. To do this requires a

program change. ON COM $ must either be disabled

or changed to generate an interrupt on each character

input. If ON COM$ is disabled, then the m ain

program has to be structured so it can process

incom ing characte rs imm ediately.

If ON COM$ generates an interrupt on each

character, then the incoming data rate should be

relatively slow (1 character every 50 ms). Note this

is not the baud rate. Th e baud rate can still be 9600.

It just should not get characters more than 20

times/second. For hand typing situations, this is just

fine.

When another computer is talking to the card,

immediate echo may not be necessary. Instead, the

incoming message can be echoed back w hen a <cr>

is received (or when ON COM$ generates an

interrupt). The cycles would merely increase based

on the command. In some ways, it becomes like a

RS-485 network described above. A comm and is

received, parsed, and processed.

Scenario 7 requires some cautionary notes. It is not

unusual to download program s through a m odem .

There is no difference between a modem down load

and one directly connected to a PC. The UI and UO

commands must be set to 1 when using COM 1 and

before going into the command mode (executing an

END or STOP statement in th e program).

A problem arises when communication is lost for

some reason. While the RPC cards have a watch

dog timer, they are not enabled during command

mode (This is true of the RPC-320 and RPC-330.)

When comm unication is lost, usually all that is

required is to redial the modem, assuming it has

been set to auto answer. If communication is lost

due to some external force (cell phone or netw ork

failure), the card will just sit there an d not ru n.

When the application is mission critical, an external

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