Another blog post

_posts/2016-12-02-the-pdp-11-and-vt100-revisited.md

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+---
+layout: post
+title: The PDP-11 and VT100 Revisited
+date: 2016-12-03 01:00:00
+permalink: /blog/2016/12/03/
+---
+
+I recently did some more work on the PCjs [VT100 Terminal](/devices/pc8080/machine/vt100/) emulation, making
+it work a bit better with other PCjs machines -- specifically, [PDP-11](/devices/pdp11/machine/) and
+[IBM PC](/devices/pcx86/machine/) machines.
+
+As I explained back in [August 2016](/blog/2016/08/03/), the PCjs VT100 emulation isn't just another VT100 emulator,
+but a simulation of the original VT100 terminal.  One of the goals is to provide users with a more authentic
+retro-computing experience, by combining classic computers with display terminals from the same time period.
+
+One of the latest improvements was a simple layout change, so that if you stretch your browser window wide
+enough, you can have your PDP-11 Front Panel and VT100 Terminal side-by-side.  It's like having Certs with Retsyn:
+TWO PCjs machines on ONE screen!
+
+[![Image of PDP-11/70 with VT100 Terminal](/blog/images/pdp-1170-vt100-side-by-side.png)](/devices/pdp11/machine/1170/vt100/)
+
+There were also a few important changes under the hood:
+
+- All PCjs machines with a SerialPort component (ie, PCx86, PC8080, and PDPjs) now support RS-232 flow control
+notifications, and changes to a port's DTR or RTS lines are communicated to the SerialPort on the other end using
+standard RS-232 DB-25 pin assignments (since every machine's internal SerialPort states are different).
+- Both the VT100 and PDP-11 terminal window support ALT-ENTER and ALT-DELETE as aliases for LINEFEED and BACKSPACE,
+since the VT100 keyboard has both RETURN and LINEFEED, as well as BACKSPACE and DELETE, and sometimes you need to use
+both (of course, you can always type CTRL-J or CTRL-H for LINEFEED or BACKSPACE, but I thought these ALT combinations
+would seem less strange to modern users).
+- The VT100 CAPS-LOCK state is now displayed alongside the standard VT100 LEDs, and PC8080 (the PCjs machine driving
+the VT100 simulation) makes a valiant effort to keep it in sync with your own keyboard's CAPS-LOCK state. 
+
+One more comment about BACKSPACE and DELETE: in the post-PDP-11, post-VT100 world of the IBM PC, BACKSPACE has come
+to mean "delete the character to the *left* of the cursor," and DELETE now means "delete the character *under* the cursor."
+
+Those are NOT what those keys meant to a typical VT100 user.  BACKSPACE was originally a *non-destructive* leftward
+movement of the cursor, whereas DELETE was a *destructive* leftward movement.  So DELETE on a VT100 is what an IBM PC
+user would think of as BACKSPACE.  To make matters worse, some modern keyboards now label the traditional BACKSPACE key
+as DELETE.
+
+With all that mind, I've tried to make the best of a bad situation, by treating your traditional BACKSPACE key as the
+VT100's DELETE key, and treating the ALT-BACKSPACE combination as the VT100's BACKSPACE key.
+
+Finally, while we're on the subject of keys, it's worth making a note of the following
+[VT100 Terminal Key Assignments](/devices/pc8080/machine/vt100/#vt100-keys):
+
+### VT100 Keys
+
+Function keys are mapped as follows:
+
+- F1: PF1
+- F2: PF2
+- F3: PF3
+- F4: PF4
+- F6: BREAK
+- F7: LINE FEED
+- F8: NO SCROLL
+- F9: SET-UP
+
+From the SET-UP screen, you can press **4** to switch to LOCAL mode and verify local operation of most VT100
+keys.  The following keys have special meaning inside SET-UP Mode.
+
+### SET-UP Mode Keys
+
+- 0: RESET
+- 2: SET/CLEAR TAB
+- 3: CLEAR ALL TABS
+- 4: ONLINE/LOCAL
+- 5: SET-UP A/B
+- 6: TOGGLE FEATURE
+- 7: TRANSMIT SPEED
+- 8: RECEIVE SPEED
+- 9: 80/132 COLUMNS
+- SHIFT-S: Save SET-UP Features
+- SHIFT-R: Restore SET-UP Features
+
+*[@jeffpar](http://twitter.com/jeffpar)*  
+*Dec 3, 2016*