Heathrow also provides power-management control functions for energy saving features included on Power Macintosh computers. The Heathrow IC is connected to the PCI bus and uses the 30–33 MHz PCI bus clock.
The Heathrow IC includes circuitry equivalent to the Ethernet, IDE, SCC, SCSI, SWIM3, and VIA controller ICs. The functional blocks in the Heathrow IC include the following:
- gated clocks PCI bus arbiter
- system wide interrupt handling
- a SWIM3 floppy drive controller
- a MESH-based (Macintosh enhanced SCSI hardware) SCSI controller
- SCC serial I/O controller
- IDE hard disk interface controller
- sound control logic and buffers
- 10Base-T Ethernet controller
The Heathrow IC provides bus interfaces for the following I/O devices:
- ADB device controller
- VIA system interface to the Cuda IC
- Screamer sound input and output IC
- 8 KB nonvolatile RAM control
The SCSI controller cell in the Heathrow IC is an 8-bit MESH controller. The MESH cell supports data transfer rates of 5 MB per second.
The Heathrow IC also contains a serial interface and sound control logic for the Screamer sound IC on the Audio/Video and Audio input/output cards.
The 85C30 SCC cell in the Heathrow IC is an 8-bit device. The SCC circuitry supports serial and LocalTalk protocols.