
Principles of Operation
44
September 2005
SCPS110
3.2
I/O Characteristics
The PCIxx12 controller meets the ac specifications of the PC Card Standard (release 8.1) and the PCI Local
Bus Specification. Figure 32 shows a 3-state bidirectional buffer. Section 14.2, Recommended Operating
Conditions, provides the electrical characteristics of the inputs and outputs.
Tied for Open Drain
OE
Pad
VCCP
Figure 32. 3-State Bidirectional Buffer
3.3
Clamping Voltages
The clamping voltages are set to match whatever external environment the PCIxx12 controller is interfaced
with: 3.3 V or 5 V. The I/O sites can be pulled through a clamping diode to a voltage rail that protects the core
from external signals. The core power supply is 1.5 V and is independent of the clamping voltages. For
example, PCI signaling can be either 3.3 V or 5 V, and the controller must reliably accommodate both voltage
levels. This is accomplished by using a 3.3-V I/O buffer that is 5-V tolerant, with the applicable clamping
voltage applied. If a system designer desires a 5-V PCI bus, then VCCP can be connected to a 5-V power
supply.
3.4
Peripheral Component Interconnect (PCI) Interface
The PCIxx12 controller is fully compliant with the PCI Local Bus Specification. The controller provides all
required signals for PCI master or slave operation, and may operate in either a 5-V or 3.3-V signaling
environment by connecting the VCCP terminals to the desired voltage level. In addition to the mandatory PCI
signals, the controller provides the optional interrupt signals INTA, INTB, INTC, and INTD.
3.4.1 1394 PCI Bus Master
As a bus master, the 1394 function of the PCIxx12 controller supports the memory commands specified in
Table 31. The PCI master supports the memory read, memory read line, and memory read multiple
commands. The read command usage for read transactions of greater than two data phases are determined
by the selection in bits 98 (MR_ENHANCE field) of the PCI miscellaneous configuration register (refer to
Section 7.23 for details). For read transactions of one or two data phases, a memory read command is used.
Table 31. PCI Bus Support
PCI
COMMAND
C/BE3C/BE0
OHCI MASTER FUNCTION
Memory read
0110
DMA read from memory
Memory write
0111
DMA write to memory
Memory read multiple
1100
DMA read from memory
Memory read line
1110
DMA read from memory
Memory write and invalidate
1111
DMA write to memory