Atari ST - Technical Specifications

Technical Specifications

All STs were made up of both custom and commercial chips:

• Custom chips:
  • ST Shifter "Video shift register chip"—Enabled bitmap graphics using 32 kB of contiguous memory for all resolutions. Screen address had to be a multiple of 256.
  • ST GLU "Generalized Logic Unit"—Control logic for the system used to connect the ST's chips. Not part of the data path, but needed to bridge chips with each other.
  • ST MMU "Memory Management Unit"— Provides signals needed for CPU/blitter/DMA and Shifter to access dynamic ram. Even memory accesses are given to CPU/Blitter/DMA while odd cycles are reserved for DRAM refresh or used by Shifter for displaying contents of the frame buffer.
  • ST DMA "Direct Memory Access"—Used for floppy and hard drive data transfers. Can directly access main memory in the ST.
• Support chips:
  • MC6850P ACIA "Asynchronous Common Interface Adapter"—Enabled the ST to directly communicate with MIDI devices and keyboard (2 chips used). 31.250 kbit/s for MIDI, 7812.5 bit/s for keyboard.
  • MC68901 MFP "Multi Function Peripheral"—Used for interrupt generation/control, serial and misc. control input signals. Atari TT030 had 2 MFP chips.
  • WD-1772-PH "Western Digital Floppy Disk Controller"—Floppy controller chip.
  • YM2149F PSG "Programmable Sound Generator"—Provided 3-voice sound synthesis, also used for floppy signalling, serial control output and printer parallel port.
  • HD6301V1 "Hitachi keyboard processor"—Used for keyboard scanning and mouse/joystick ports.