PCI950

IRQSER DESERIALIZER

SCPS015A – JULY 1997 – REVISED JANUARY 1998

3

POST OFFICE BOX 655303

functional description

The PCI950 accepts the serialized IRQ stream from the PC Card controller for conversion to discrete ISA and

PCI interrupts. The serialized IRQ protocol is defined in the document Serialized IRQ Protocol for PCI Systems,

revision 6.0. This protocol uses a serial packet consisting of one start frame, several IRQ/data frames, and one

stop frame.

Start frame: There are two modes of operation for the IRQSER start frame – quiet mode and continuous mode.

During continuous mode the PCI950 initiates the start frame. A low level on the POLLMODE input pin selects

the quiet mode and a high level selects continuous mode for the PCI950. The total low-pulse width on a start

frame is eight clocks. After reset the PCI950 defaults to continuous mode.

IRQ/data frame: The PCI950 is designed to decode a fixed length of 21 IRQ/data frames that are sampled in

the following sequence: IRQ0, IRQ1, SMI, IRQ3 through IRQ15, IOCHK, INTA, INTB, INTC, and INTD.

Stop frame: After the completion of a start frame and 21 IRQ data frames, the PCI950 generates a stop frame.

The pulse width of the stop pulse is determined by the status of the POLLMODE input pin sampled during the

start frame.

IRQ0

IRQ1

IRQ2

IRQ3

IRQ4

– – –

IRQ3

(see Notes 2 and 3)

RR

R

R

R

R

TT

T

T

T

T

SS

S

S

S

2

PCI950

None

PCLK

IRQSER

DRIVE

Legend:

None

Start Frame

R = Recovery

S = Sample

T = Turnaround

NOTES:

2. Start frame is eight clocks in duration.

3. Slave or host initiated: POLLMODE is level dependent.

Figure 1. IRQSER Start-Frame Timing

IRQ15

IOCHK

INTA

INTB

INTC

IRQ15

(see Notes 4 and 5)

R

RR

R

R

R

T

TT

T

T

T

SS

S

S

S

PCI950

None

PCLK

IRQSER

DRIVE

I = Idle

INTD

RT

S

(see Note 6)

Stop Frame

I

Legend:

R = Recovery

S = Sample

T = Turnaround

I

NOTES:

4. The PCI950 stop pulse is two or three clocks in duration.

5. There may be none, one, or more idle states during the stop frame.

6. When the PCI950 is in continuous mode, there are 17 idle states between the stop frame and the start frame.

Figure 2. IRQSER Stop-Frame Timing