Editing Atari 1040ST (section)

== Custom Chip Set ==

The Atari ST uses a set of four custom ASICs alongside standard off-the-shelf components. These custom chips are the most failure-prone components in the system and are no longer manufactured.

<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table"
! Chip !! Part Number !! Package !! Function
|-
| '''GLUE''' || C025915-38A || PLCC-84 || System "glue logic." Generates active display timing, address decoding for I/O and ROM, handles interrupt prioritisation, bus error generation, and DMA request arbitration. Directly controls VPA, DTACK, and bus signals.
|-
| '''MMU''' || C025912-38 || PLCC-68 || Memory Management Unit. Generates RAS/CAS signals for DRAM, handles DRAM refresh, produces video DMA addresses for the Shifter, and manages the memory map configuration.
|-
| '''Shifter''' || C025914 || DIP-40 || Video shift register. Reads video data from DRAM (via MMU), serialises it into pixel data for the monitor output, and manages the 512-colour palette (16 palette registers × 9 bits). Directly drives the analogue RGB output.
|-
| '''DMA''' || C025913 || DIP-40 || DMA controller for floppy disk (WD1772) and ACSI hard disk interface. Provides sector-count-based transfers between disk controllers and system RAM.
|}