Qedit

RCRTSTRAPSGH for Handshaking

The G and H straps of the HP terminal control datacomm handshaking. If you pull up your Terminal Config screen, it should look something like this:

  InhHndShk(G) NO       Inh DC2(H) NO  

Since these are “inhibit” straps, NO actually means “yes, do the handshake”. G and H control whether the terminal waits for a DC1 and/or DC2 prompt character from the computer before sending input, such as on terminal status requests or upon pressing Enter in block-mode. If the straps are configured incorrectly, the symptom is a hung terminal (i.e., the terminal is waiting for a prompt character that is never going to come, or the terminal has sent the data before the computer was ready because it didn’t wait for the prompt).

By default, Qedit sets these straps the way it appears will work best, based on your CPU and Term Type. The settings differ between Line mode and Visual mode.

Line Mode. Qedit starts execution in Line mode and immediately attempts a status check of your terminal. With a DTC or ATP, this usually requires a handshake, so Qedit should set G and H to NO. If you are using an X.25 network or a LAN, the network provides buffering of data sent by the terminal, so Qedit usually inhibits handshaking. These Line mode rules apply to both MPE V and MPE/iX.

  G=NO, H=NO  

  G=YES, H=YES  

Block-Mode. The situation in Visual mode is more complicated. You are in block-mode and when you press Enter, your terminal wants to send a screen of memory. To summarize the recommended G and H values:

  G=YES, H=NO  

  G=YES, H=YES  

  G=YES, H=YES  

  G=YES, H=YES  

MPE V has a complex system to stop your terminal from sending the data until the ATP is ready and there are enough memory buffers available in the CPU. The terminal sends a DC2 when you press Enter and MPE replies with an Escape code to Home Up and a DC1 to trigger the transfer. This arrangement only works if G=YES and H=NO.

MPE/iX improves the speed of block transfers by eliminating the Home Up and the DC1 trigger. Instead of sending a Home Up Escape code, MPE/iX enables a terminal option to do an automatic Home Up when you press Enter. That is why block-mode does not work on some older terminals. Instead of the DC1, the DTC provides a typeahead buffer for the entire screen contents when you press Enter in block-mode. Qedit sets G=YES, H=YES to inhibit handshaking on a DTC while in block-mode. However, the DTC does not have unlimited buffer space, so it uses XON/XOFF pacing to control the flow from the terminal. You must enable your terminal’s XON/XOFF Transmit Pacing, which is not enabled by default.

Using block-mode over an X.25 network or LAN can be tricky. Theoretically, the network provides full buffering and no handshaking is needed, so set G=YES and H=YES on both MPE V and MPE/iX. However, the buffers may not be large enough for the transfer that Qedit makes in Visual. MPE/iX must work with the network to ensure that the terminal is configured to do an automatic Home Up on Enter, otherwise the terminal starts transferring from the position of the cursor at the time you press Enter.

Overriding Qedit. If you are using an unusual X.25 network to connect your terminal to the HP e3000, you may find that Qedit sets G and H incorrectly. Perhaps the network simulates a direct connection so well that Qedit cannot figure out that you are using X.25.

For these situations, Qedit has a JCW that allows you to specify exactly how you want G and H set in Line mode.

  :setjcw rcrtstrapsgh = n  

Qedit only reads and never changes the value in this JCW.

To override the setting of G and H in Visual mode, use the Set Vis DTC option, setting it ON or OFF. You may have to experiment to find the right setting.

G & H Summary. In block-mode, Qedit decides how to set G and H. You can override that decision by doing Set Vis Classic On or Set Vis DTC On. When Qedit returns to Line mode, it needs to reset the G and H straps to some value. Again, Qedit makes a choice of its own, but it may not work on all networks. Therefore, the JCW allows you to override the reset values for G and H when exiting from full-screen mode to Line mode.

Trivia. These settings are called “straps” because in the earliest HP terminals, configuration settings were enabled or disabled by inserting a short piece of wire (no bigger than a staple) between two holes in the circuit board. Configuring by way of these short metal “straps” became known as “strapping your terminal”. Today, of course, all configuration is done in terminal software by way of on-screen menus.

RCRTSTRAPSGH for Handshaking