PCI Bus Pin Out, [Parallel Bus]

PCI Bus pinout for both 32 bit and 64 bit cards is shown below;
Signal Pins 63-94 are only used on 64 bit PCI bus cards. The PCI pinout for the 32 bit bus stops at the key-way [Spacer], while the 64 bit pin out occupies the entire table. The PCI local bus was used in personal computers to provide expansion slots for add-on cards to the motherboard.
The PCI bus replaced the ISA PC-AT expansion slot in PCs.
The PCI local bus is not the same as the new PCI Express bus which has a completely different pinout.

Peripheral Component Interface Pinout

The number sign in the pinout table below refers to: "A # symbol at the end of a signal name indicates that the signal’s asserted state occurs when it is at a low voltage. The absence of a # symbol indicates that the signal is asserted at a high voltage.

Designer note; the pinout provided on this page relates to the PCI main board connector on the mother board.
Add-in cards [daughter boards may have a slightly different connector pin out.

PCI Connector Dimensions

RST# [input] Reset is used to bring PCI-specific registers, sequencers, and signals to a consistent state.

CLKRUN# [input] [Open Drain, Tri-state] Clock running is an optional signal used as an input for a device to determine the status of CLK.

M66EN [input] The 66MHZ_ENABLE pin indicates to a device whether the bus segment is operating at 66MHz or 33 MHz.

AD[31::00] [Tri-state] Address and Data are multiplexed on the same PCI pins. A bus transaction consists of an address phase followed by one or more data phases. The Time Multiplexed Address and Data bus may exist as either 0 to 31 bits (32bits) or 0 to 63 bits (64bits) using the 64 bit expansion bus. Both the Address and Data line use the same bus, Address first then Data. 32 bit PCI may also use 64 bit addressing by using two address cycles; termed Dual Address Cycles (DAC), the low order address is sent first. Additional control bits are utilized once the bus is increased to 64 bits.

PME# The Power Management Event signal is an optional signal that can be used by a device to request a change in the device or system power state.

FRAME# [Sustained Tri-State] Cycle Frame is driven by the current master to indicate the beginning and duration of an access.

IRDY# [Sustained Tri-State] Initiator Ready indicates the initiating agent's (bus master's) ability to complete the current data phase of the transaction. IRDY# is used in conjunction with TRDY#.

TRDY# [Sustained Tri-State] Target Ready indicates the target agent's (selected device's) ability to complete the current data phase of the transaction. TRDY# is used in conjunction with IRDY#.

STOP# [Sustained Tri-State] Stop indicates the current target is requesting the master to stop the current transaction.

LOCK# [Sustained Tri-State] Lock indicates an atomic operation to a bridge that may require multiple transactions to complete. When LOCK# is asserted, non-exclusive transactions may proceed to a bridge that is not currently locked.

INT# [Open Drain] Interrupts on PCI are optional and are "level sensitive," asserted low (negative true).
--- INTA#, INTB#, INTC#, INTD#

PAR [Tri-state] Parity is even parity across AD[31::00] and C/BE[3::0]#. Parity generation is required by all PCI agents. PAR is stable and valid one clock after each address phase.

PERR# [Sustained Tri-State] Parity Error is only for the reporting of data parity errors. Two Parity lines are made available, one for the 32 bit bus width (bits 0 to 31) and an additional one for the 64 bit expansion (bits 32 to 63). Two error bits; I assume, 1 for the LSB 32 bits and one for the upper 32 bits.

REQ# [Tri-state] Request indicates to the arbiter that this agent desires use of the bus. This is a point-to-point signal. Every master has its own REQ# line.

GNT# [Tri-state] Grant indicates to the agent that access to the bus has been granted. The GNT line is a point-to-point signal, each master has its own GNT# signal.

IDSEL [input] Initialization Device Select is used as a chip select during configuration read and write transactions.

DEVSEL# [Sustained Tri-State] Device Select, when actively driven, indicates the driving device has decoded its address as the target of the current access.

SERR# [Open Drain] System Error is for reporting address parity errors, data parity errors on the Special Cycle command, or any other system error.

C/BE[3::0]# [Tri-state] Bus Command and Byte Enables are multiplexed on the same PCI pins. During the address phase of a transaction, C/BE[3::0]# define the bus command.

The specification defines both a Reset line and a Clock line. The Clock may be either 33MHz or 66MHz. I believe the 66MHz clock rate is only defined for the 64bit bus width.
A number of 'Handshake' lines exist to allow communication, i.e. Ready, and Acknowledge, see pin out above.

JTAG The JTAG interface is optional on the PCI bus. Add-in cards [expansion boards] that do not implement the JTAG Boundary Scan are required to connect [short] TDI and TDO (pins 4A and 4B) so the scan chain is not broken.

The pinout listings showing (+5 V or +3.3 V) mean: In a +5 volt system the pins are +5 volts, in a +3.3 volt system the pins are +3.3 volts.

64-Bit Bus Extension
PCI supports a high 32-bit bus, referred to as the 64-bit extension to the standard low 32-bit bus.
The high 32-bit extension for 64-bit devices needs an additional 39 signal pins: REQ64#, ACK64#, AD[63::32], C/BE[7::4]#, and PAR64.

PAR64 Parity bit, even parity. Parity generation is required by all PCI agents. PAR is stable and valid one clock after each address phase. PAR64 covers AD[63::32] and C/BE[7::4]# and has the same timing and function as the PAR bit. PAR64 requires a pull-up resistor when 32-bit transactions are used. When PAR64 is not used the line will float to the threshold level causing oscillation or high power drain through the input buffer.

REQ64# [Request-64] is bused to all devices on the system board (including PCI connector slots) that support a 64-bit data path and indicate that the Bus Master wants to make a 64-bit transfer. This signal has a single pull-up resistor on the system board.

ACK64# [Acknowledge 64-bit Transfer] is bused to all 64-bit devices and slots on the system board and pulled up with a single resistor located on the system board. ACK64# is actively driven by the device that has positively decoded its address as the target of the current access, indicating that the target is willing to transfer data using 64 bits.

AD[63::32], Note these are Tri-state lines and require a pull-up resistor during 32-bit transactions to keep the nets from floating. The upper Address and Data bits are multiplexed on the same pins and provide 32 additional bits. During an address phase (when using the DAC command and when REQ64# is asserted), the upper 32-bits of a 64-bit address are transferred; otherwise, these bits are reserved.

C/BE[7::4]#, [Bus Command and Byte Enable] Note these lines Tri-state and require a pull-up resistor during 32-bit transactions to keep the nets from floating. The Bus Command and Byte Enable lines are multiplexed on the same pins. During an address phase (when using the DAC command and when REQ64# is asserted), the actual bus command is transferred on C/BE[7::4]#; otherwise, these bits are reserved and indeterminate. During a data phase, C/BE[7::4]# are Byte Enables indicating which byte lanes carry meaningful data when a 64-bit transaction has been negotiated by the assertion of REQ64# and ACK64#.

Back to the main PCI Bus page, or the PCI Board Dimension page PCI Card Size or Personal Computer bus page.

PRSNT[1::2]# Add-in card Present
Note; PRSNT1 [B9] and PRSNT2 [B11] are present detect pins used just to detect the presence or absence of a PCI card. The PRSNT# pins relate only to the PCI connector.

Mother boards must decouple both of these pins individually to ground with 0.01 uF capacitors, because one or both of the pins also provide an AC return path. These pins may not be bused or connected to each other on the system board. Further the PRSNT# pins on the system board is optional. If the system board design accesses these pins to obtain add-in card information, each pin must have an appropriate pull-up resistor (of approximately 5 k ohm) on the system board.

Description of PCI pins and signal names'

The Peripheral Component Interface 'PCI' Bus was originally developed as a local bus expansion for the PC (ISA) bus. The PCI spec defines the Electrical requirements for the interface. No bus terminations are specified, the bus relies on signal reflection to achieve level threshold. The first version of the PCI bus ran at 33MHz with a 32 bit bus (133MBps), the current version runs at 66MHz with a 64 bit bus. The PCI bus operates either synchronously or asynchronously with the mother board bus rate. While operating asynchronously the bus will operate at any frequency from 66MHz down to (and including) 0Hz. Flow control is added to allow the bus to operate with slower devices on the bus, allowing the bus to operate at their speed. PCI is an unterminated bus, the signal relay on signal reflections to attain there final value.

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