Signetics 2513

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The Signetics 2513N.

The Signetics 2513 is a character generator developed by Signetics around 1970 which renders characters on a display screen and was used as the video chip for several early 8-bit devices. The most common character set supports uppercase letters, numbers, and some punctuation and mathematics symbols, but several different character sets were sold, and custom sets could be purchased.

Signetics produced a couple other similar chips including the 2516 which was made for vertical raster displays instead of the 2513's horizontal raster, and the 2526 which supported characters with a slightly higher resolution.

General Instrument produced a similar series of chips called the General Instrument RO-3-2513, which were direct replacements for the Signetics 2513 line.

Personal

I learned about the Signetics 2513 while reading about the Apple I. The more I read about the chip, the more intriguing I found it.

Technical

The chip can display 40×24 characters on a screen and store 64 monochrome bitmaps, each with a resolution of 8×5 pixels, in its ROM. These bitmaps cannot be modified, however, for a fee, the company allowed customers to send in punch cards with custom bitmaps drawn on them, and Signetics would mail back ROM chips loaded with their custom characters. The chip was sold in two packages: silicon or ceramic, signified N and I respectively, both in a DIP.

Devices

Several devices are known to have used the Signetics 2513 including:

Date Device Character Set Code
1973-09-?? TV Typewriter CM2140
1975-??-?? Intel SDK-80 CM2140
1976-04-11 Apple I CM2140
1977-06-10 Apple II (early models) CM2140
197?-??-?? Early Atari arcade cabinets  ?

Characters

Since it is a ROM, the 2513 could not be modified after it was manufactured. However, to appease customers, Signetics sold at least five different character sets which could be ordered by their code number (prefixed with "CM"). Below are the five different character sets sold by Signetics.

CM2140

The most popular character set sold by Signetics was code number CM2140 which was based on the ASCII table. Although Signetics advertised the chip as supporting ASCII, it could only store 64 characters to ASCII's 128. However, it could still convey most of the table since 33 ASCII characters are non-printable, and lowercase letters make up another 26. Of the symbols, it's only missing the pipe (|), backtick (`), tilde (~), and braces ({, }). The order of the characters is similar to ASCII, but the structure moves the letters before numbers and punctuation. The CM2140 also uses the less popular 1967 ASCII set instead of the far more popular 1965 set.

Character Set Rendered
0 1 2 3 4 5 6 7 8 9 A B C D E F
0x @ A B C D E F G H I J K L M N O
1x P Q R S T U V W X Y Z [ \ ] ^ _
2x  ! " # $  % & ' ( ) * + , - . /
3x 0 1 2 3 4 5 6 7 8 9  :  ; < = >  ?

Signetics 2513 - CM2140 - Characters.png

CM2170

A Signetics catalog describes this character set as having a yen (¥) symbol. I haven't been able to find at actual lookup for it, but I assume it replaces the dollar sign.

0 1 2 3 4 5 6 7 8 9 A B C D E F
0x @ A B C D E F G H I J K L M N O
1x P Q R S T U V W X Y Z [ \ ] ^ _
2x  ! " # ¥  % & ' ( ) * + , - . /
3x 0 1 2 3 4 5 6 7 8 9  :  ; < = >  ?

CM3021

Code CM3021 includes the lowercase letters as well the ASCII punctuation missing from the CM2140 set. Since the printable ASCII set is now complete with this chip, it fills in the remaining space with a variety of arrows and symbols. A computer could be designed with the CM3021 combined with the CM2140 in order to give the display a complete ASCII table.

Character Set Rendered
0 1 2 3 4 5 6 7 8 9 A B C D E F
0x 🕭 ·̲
1x 🅴
2x ` a b c d e f g h i j k l m n o
3x p q r s t u v w x y z { | } ~

Signetics 2513 - CM3021 - Characters.png

CM3030

Code CM3030 is described in a Signetics catalog as using the "old" ASCII set, which, I presume means the 1965 set. This would replace the at (@) with a back tick (`) and the backslash (/) with a tilde (~), but I can't verify this.

0 1 2 3 4 5 6 7 8 9 A B C D E F
0x ` A B C D E F G H I J K L M N O
1x P Q R S T U V W X Y Z [ ~ ] ^ _
2x  ! " # $  % & ' ( ) * + , - . /
3x 0 1 2 3 4 5 6 7 8 9  :  ; < = >  ?

CM4800

Code CM4800 uses a Katakana character set. The order is cut in half, starting at the T line instead of with the pure vowels, and a few of the glyphs are out of order. The set only features the base glyphs, modifiers are separate characters, so combined glyphs like ga (ガ) must be written as (カ゛). Also, due to being limited to only 64 characters, not all of the common punctuation is included.

Character Set Rendered
0 1 2 3 4 5 6 7 8 9 A B C D E F
0x
1x
2x
3x

Signetics 2513 - CM4800 - Characters.png

Media

Documentation

Links