GE A20B-0008-0430/04A CRTC Board

This board manages CRT display output and tape puncher interface for GE CNC systems. It generates character-based video signals for operator console screens. Additionally, it controls paper tape puncher devices for program storage.

Technical Specifications of GE A20B-0008-0430/04A

The GE A20B-0008-0430/04A measures 27.0 cm in length and 20.0 cm in width. Its board weight equals approximately 0.55 kg for straightforward rack mounting. Two 50-pin male connectors link this board to the CNC backplane. Furthermore, the board provides separate interfaces for video and puncher devices.

Parameter	Specification
Brand	General Electric (GE)
Full Model	A20B-0008-0430/04A
Category	CRTC/Puncher Circuit Board
Dimensions (L x W)	27.0 cm x 20.0 cm (10.63″ x 7.87″)
Board Weight	0.55 kg (1.21 lbs)
Backplane Connectors	2 x 50-pin Male Headers
Video Output	1 x 9-pin D-Sub Female (CRT Monitor)
Puncher Interface	1 x 25-pin D-Sub Female (Parallel)
Video Signal Type	Composite Video or TTL RGB (Jumper Selectable)
Display Resolution	24 Lines x 80 Characters (Text Mode)
Character Generator	On-Board ROM (256 Characters, 7×9 Dot Matrix)
Puncher Protocol	Centronics Parallel (Compatible)
Puncher Data Rate	Up to 200 Characters per Second
Puncher Control Lines	STROBE, BUSY, ACK, PAPER OUT, ERROR
On-Board Components	1 CRTC Chip (Motorola 6845) + 1 Character ROM + 2 UARTs + 4 Line Drivers + 8 Protection Diodes
Memory Resources	2 kB Video RAM (Static) + 1 kB Buffer RAM
Energy Storage	4 x 10 µF Tantalum Capacitors (25V) + 2 x 100 µF Electrolytic (16V)
Operating Voltage	+5 VDC, +12 VDC from Backplane
Power Consumption	3.2 W (Typical)
Video Refresh Rate	60 Hz (Non-Interlaced)
Operating Temperature	0°C to +50°C (32°F to 122°F)
Status Indicators	2 Green LEDs (Video OK + Puncher Ready)

Energy Storage and Video Signal Generation

The GE A20B-0008-0430/04A stores energy using six onboard capacitors. Four tantalum capacitors filter noise from the CRTC and video RAM circuits. Two electrolytic capacitors provide hold-up energy for the puncher interface drivers. Consequently, this board maintains stable video display during tape punching operations.

CRTC Operation and Character Display

The Motorola 6845 CRTC chip controls all video timing and refresh functions. A dedicated character ROM stores the 7×9 dot matrix font patterns. The board generates composite video or TTL RGB signals for CRT monitors. Thus, operators can read CNC status and program data clearly.

Puncher Interface and Parallel Communication

This board includes a Centronics-compatible parallel port for tape punchers. The interface uses standard STROBE, BUSY, and ACK handshake signals. Four line drivers boost output signals for reliable long-distance communication. Therefore, the board connects directly to legacy paper tape punchers without adapters.