Measurement-computing Personal488 rev.3.0 For DOS & Windows 3.Xi Manual de usuario descargar pdf (Pagina 131)

8M. Data Transfers II. SOFTWARE GUIDES - 8. Driver488/DRV

II-116 Personal488 User’s Manual, Rev. 3.0

This reads data into

until either

characters have been received, or

EOI

has been detected.

However, if

EOI

causes the transfer to stop, we can discover how much data has been received by using

the

BUFFERED

command:

PRINT#1,"BUFFERED"

INPUT#2,N

The number of bytes transferred is read into

. Now we can use this value to send the read data out to

device

PRINT#1,"OUTPUT17#";N;"BUFFER";VARSEG(W%(1));":";VARPTR(W%(1));"EOI"

Note that the variable

has been used in place of the literal

to specify how many bytes to transmit.

Clearly,

BUFFERED

I/O is more complex than simple direct I/O. However, it can be very useful.

BUFFERED

I/O is normally much faster than direct I/O because the characters go directly from memory

to the bus under the control of Driver488/DRV without the intervention of BASIC or DOS. Also,

BUFFERED

I/O is not limited by the 255-character limit on

INPUT$

that can hinder binary

ENTER

Asynchronous Transfers

Driver488/DRV can return to the user’s program while a transfer is in progress. This is useful

whenever the transfer takes a substantial amount of time, and other processing could proceed while

waiting. For example, suppose a certain bus device can transfer only 1000 bytes per second. If there

are 10,000 bytes to transfer, it takes 10 seconds to complete the transfer. The following statements

might be used to receive this data:

DIM R%(5000)

PRINT#1,"ENTER 09 #10000 BUFFER"; DS%;

“:”; VARPTR(R%(1)); “CONTINUE”

Now do other work while

the transfer is continuing

PRINT#1,"WAIT"

The

CONTINUE

keyword tells Driver488/DRV to return to the program after setting up the transfer.

The program is then free to do other processing, as long as it does not need access to the IEEE 488 bus.

Finally, when the program is ready to process the received data it performs a

WAIT

to check that the

data has been completely received. In this way,

CONTINUE

transfers overlap IEEE 488 bus data

transfers with program execution.

The use of DMA and interrupts requires proper hardware and software configuration. For more

information, refer to the Sub-Chapter “Installation & Configuration” early in this Chapter.

8N. Operating Modes

Topics

• Introduction...................................................................................II-116

• Operating Mode Transitions......................................................II-116

• System Controller Mode..............................................................II-117

• System Controller, Not Active Controller Mode....................II-117

• Not System Controller Mode......................................................II-119

• Active Controller, Not System Controller Mode....................II-119

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