RECV3270

Description

The RECV3270 intrinsic performs 3 functions:

With standard (wait) MPE I/O, the RECV3270 intrinsic suspends your program until data arrives from the host or until the timeout interval specified in the OPEN3270 intrinsic has expired.

If your program calls the RECV3270 intrinsic without having set the receive timeout, and the host does not send any data, your program will be suspended indefinitely. Therefore, you should always set the receive timer portion of the timeout parameter of the OPEN3270 intrinsic to ensure that your program can regain control after an unresolved RECV3270 call.

If your program is emulating an IBM 3278 display station (LU.T2) with standard I/O, a call to RECV3270 suspends processing until a transmission arrives from the host. Then, RECV3270 updates a counter telling SNA IMF that your program has seen the most recent internal screen image.

SNA IMF/XL and SNA IMF/V handle LU.T2 emulation differently. When a new transmission arrives from the host, SNA IMF/XL does not update the internal screen image unless your program has called RECV3270 and is waiting for data from the host. If your program has not called RECV3270, SNA IMF/XL waits for a RECV3270 call before it updates the internal screen image. SNA IMF/V updates the internal screen image whether or not your program has called RECV3270.

	NOTE: With no-wait I/O, you must follow each call to RECV3270 with a call to IOWAIT, IOWAIT3270, IODONTWAIT, or IODONTWAIT3270.

If SNA IMF/V receives host data and updates the internal screen image before your program calls RECV3270, it can tell from the counter that your program has not read the internal screen image since the last host transmission. If your program then calls, for example, READFIELD (or any intrinsic that accesses the internal screen image), SNA IMF/V will return a result code of 9, indicating that the host has updated the internal screen image since the last time your program received it.

Result code 9 tells your program that the field it just attempted to read belongs to a different screen image from the data it read previously. Whenever your program receives result code 9, it should call RECV3270. SNA IMF/V then updates the counter and allows your program to access the most recent screen image.

SNA IMF/XL does not return a result code of 9, so you must check the result parameter after a call to RECV3270 to determine whether the host has sent new data. If result = 0, the host has sent new data, and the internal screen image has been updated. If result = 24, the receive timer has expired, and the internal screen image has not been updated.

If your program is emulating a printer (LU.T1 or LU.T3), the RECV3270 intrinsic can prevent the IBM host from sending new data before your program has a chance to process the current screen image.

Ordinarily, SNA IMF sends a positive response to the IBM host after it receives a transmission, whether or not your program has called RECV3270. However, during printer emulation, SNA IMF delays sending its positive response until your program processes the new data and calls RECV3270 again.

During printer emulation (with standard I/O), the first call to RECV3270 suspends your program until data has arrived for it, then it informs your program that the host has updated the internal screen image. Your program can then call other SNA IMF intrinsics to check the screen, locate field attributes, read data, and so on, while the host is still waiting for a positive response. When your program has finished processing the current screen image, it must call RECV3270 again. This RECV3270 call tells SNA IMF that your program is finished processing and is ready for more data. SNA IMF then sends a positive response to the IBM host, and the host can continue transmitting.

After your program calls the OPEN3270 intrinsic, it must immediately call the RECV3270 intrinsic. This first RECV3270 call receives the SNA IMF banner screen from the OPEN3270 intrinsic. This first internal screen image can be discarded, and you can continue with your processing.

In most cases, you should follow a call to TRAN3270 with a call to RECV3270 to receive any data that the host sends in response to your transmission. However, if you know that the host will not respond to your transmission, you can call RESET3270 to reenable the keyboard. (Successful calls to TRAN3270 disable the keyboard.)

The host might update the screen in more than one transmission. To ensure that you always receive a complete screen from the host, you might need to write your program to issue a variable number of RECV3270 intrinsic calls.

If the host system always sends a keyboard enable in the last transmission, you can set the keyboard enable timer in your call to the OPEN3270 intrinsic. Then you need to call RECV3270 only once to receive a complete screen image. The RECV3270 intrinsic will not complete until the keyboard enable has been received or the timer has run out.

	NOTE: Be aware of any changes in your host system software. For example, TSO always sends the keyboard enable timer in the last transmission, but other applications might not. Also be aware of changes in protocol. If you migrate from BSC to SDLC, more host transmissions are involved in starting your SNA session. You may need to modify the logon routine in your program to issue more RECV3270 intrinsic calls when an SNA session is initiated.

The RECV3270 intrinsic can be called in either transparent or non-transparent mode.

With no-wait I/O, your program can call RECV3270 for several different devices. It can then call IOWAIT or IOWAIT3270, and it will suspend processing until data has arrived for one of the devices.

After calling RECV3270 with no-wait I/O, your program can call IODONTWAIT or IODONTWAIT3270, instead of IOWAIT or IOWAIT3270, and it will not be suspended. Each time your program calls IODONTWAIT or IODONTWAIT3270, SNA IMF checks to see if data has arrived for a device and informs your program. If no data has arrived, your program continues processing, and it must call IODONTWAIT or IODONTWAIT3270 again later to see if data has arrived.

With no-wait I/O, every call to RECV3270 must be followed by a call to IOWAIT, IOWAIT3270, IODONTWAIT, or IODONTWAIT3270. Result codes that would be returned through the RECV3270 intrinsic with standard wait I/O are returned through the IOWAIT, IOWAIT3270, IODONTWAIT, and IODONTWAIT3270 intrinsics with no-wait I/O.

For more information on using the ECV3270 intrinsic with no-wait I/O, see Chapter 4 “Intrinsics Used with No-Wait I/O”

{************************** Global Declarations **************************}type   shortint      = -32768..32767;       { global type, two bytes (half word) }...var   terminalid    : shortint;          { value returned by OPEN3270 intrinsic }   result        : shortint;...procedure RECV3270;  intrinsic;...{************************** Intrinsic Call **************************}RECV3270 (terminalid, result);