Micro­power

others, for example DEF, can only operate in indirect mode.

The command LIST instructs the computer, to display the lines it has stored. It will normally display 5 lines at a time, but this can be changed by entering the command LINES x, where x is the number you wish to display. The number x refers to stored Basic lines, not to screen lines; thus if any of the program lines contains more than 48 characters (see below), data may be scrolled off the screen even if the value of LINES is less than 15. The value of LINES will remain unchanged until a new value is entered, or until you do the next ‘cold start’ of Basic, when it will be reset to the default value of 5.

You can break out of a listing at any point by typing ‘escape’ (shift/​enter). You can also start a listing at any particular line merely by adding the appropriate line number to the LIST command. For example, LIST 800 will list the program from line 800. The LIST command is particularly useful for editing purposes, because if you are using Nas-Sys, any line on the screen can be modified as required, and when you press enter the new version replaces the old, just as if you had re-entered the whole line (which you would have to do with most micros). However, if you break out of a program (with ‘escape’) and then LIST in order to edit the program, be sure to clear the screen first, because the interpreter will accept all the characters on a line, including any left behind by the program, and some very peculiar lines can be produced, particularly when there are graphics characters on the screen.

Line Format

The Nascom screen holds 16 lines of 48 characters. If you type in a Basic line which, including the line number and any spaces in the line, is exactly 48 characters long, as the last character is typed the cursor will move to the start of the next line. However, the line will not have been stored, because storage does not occur until the ‘enter’ key is pressed. You must return the cursor to some point on the original line (anywhere will do) and then press ‘enter’. In fact, Nascom Basic will accept up to 72 characters on a line, but the power and flexibility of Nas-Sys screen editing is lost once you exceed 48. One method of entering more than 48 characters per line is to enter the one-byte graphics codes which represent the Basic reserved words. For example, pressing the space bar with the graphics key depressed give code £A0, which represents the command LIST. The PRINT command is a special case – this can be entered by typing a question mark (the reserved word is not, of course, stored as a question mark, the code is actually £9E). Try entering a line number, followed by a series of question marks separated by colons. Enter the line and list the program – you will see that the interpreter produces a series of PRINT commands. However, you will find that any characters that overflow the first line will be lost when you try to edit this monster. If you look in the computer’s memory by entering T10F8 1110 from the monitor you will see a series of £9E codes, separated by £3As, which is how the Basic interpreter stores the line.

Another method of entering longer lines is to use the monitor’s X command, which controls the serial output. Return to the monitor by pressing reset, enter X0, and