CDTV-CR Hardware Registers

The CDTV-CR is the bridge chip on the Amiga CDTV that connects the internal IDE bus to the CDGS CD-ROM controller (cdgs.md). It sits at $A40000 on the CDTV motherboard.

This page documents the limited public information available for the CDTV-CR. The chip is essentially treated as a transparent bridge by the CDTV system software; only one bit is commonly referenced in hardware documentation.

Base address

CDTV_ADDR    =    $a40000

Register / bit definition

Bit Define Meaning
0 CDTV_IDE IDE interrupt present — flag indicating IDE activity from the CD-ROM drive, presumably bit 0 of a status register at the base address

AT register mapping (CDTV)

The CDTV uses the same AT_* register set as the A300/A600/A1200 — see at-ide.md — but offset from $A40000 instead of from $DA2000. The same register constants apply:

Offset Name Access Description
$00 AT_Data RW (16-bit) Data port
$04 AT_Error R Error register
$08 AT_SectorCnt RW Sector count
$0C AT_SectorNum RW Sector to start (1-based)
$10 AT_CylLow RW Low cylinder
$14 AT_CylHigh RW High cylinder
$18 AT_DriveHead RW Drive + head
$1C AT_Status R Status (clears interrupt)
$1C AT_Command W Command (starts drive)
$1000 AT_IntStatus R Interrupt status bit, active LOW
$1018 AT_AltStatus R Alternate status
$1018 AT_DeviceCtrl W Device control
$101C AT_DriveAddress R Drive address

On CDTV, these resolve to the absolute addresses $A40000–$A4101C (instead of $DA2000–$DA301C on A600/A1200).

Limitations

The full CDTV-CR register map (and its relationship to CDGS at $B80000) is not widely documented — the chip is essentially treated as a transparent bridge. For a complete picture of CDTV motherboard glue logic, external documentation would be needed.

Cross-references