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Comment by qznc

9 years ago

There is more to it.

For example, note that the numerals map to their direct binary notation plus a 011 in front. 0 => ...0000, 1 => ...0001, 2 => ...0010, etc.

Now I wonder, why don't they start in the zero row? In other words, why is 0 = 0110000, instead of 0100000?

Why are the parens not in the same row as braces and brackets?

Why isn't "&" (ligature of "et") not in the same row as "e"? "$" ("dollar") is in the same row as "d".

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qznc

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kps  9 years ago

The 1963 standard⁰ answers your questions. (Probably the final 1967 version does too, but it's not online anywhere.)

In this instance the more common 8-column presentation actually better reflects the design. It's important that the low 4 bits of '0' are 0. The 0x2X column and 0x3X column are related by shift (on some devices²).

⁰ http://worldpowersystems.com/archives/codes/X3.4-1963/index....

¹ https://en.wikipedia.org/wiki/Binary-coded_decimal

² https://en.wikipedia.org/wiki/Bit-paired_keyboard

pvg  9 years ago

You have a typo in the code for zero, it doesn't end with 1. The reason 0 can't be 0100000 is that's the start of the printable characters and an established standard/requirement was that space collate below all other printable characters. So you have to start with space, you can't put 0 there.

danielweber  9 years ago

> Why isn't "&" (ligature of "et") not in the same row as "e"? "$" ("dollar") is in the same row as "d".

It matches old mechanical typewriters. I have one with the shift-characters over the numbers being exactly what was 16 characters (one bit flip) away in the table.