Re: 64-bit on-board devices on 32-bit PCI bus

["Venkateshwarlu V" <venkateshwarluv@myw.ltindia.com>]

** Proprietary **

Hello Mr.Anand,
I will try to answer ur questions here.

Should i provide on-board pull-ups on the upper 32-bit extension or just leave
them unconnected?
U should not provide any on-board pull-ups, incase if u use same extension board for 64-bit connector, there are pull-ups for all the data lines on mother-board also, due to two pull-ups on each data line, there will be more pull-up current. So upper 32-bits must be unconnected.
 I personnaly feel that the 32-bit extension of these individaul devices should
be left unconnected (hoping that the devices will take care of preventing the
bus from floating).
The device cannot take care of preventing from floating
 The other thing i thought if i provided a common on-board
pull-up for the 32-bit extension of both these devices is that there could be
probable data contention, because at any time and on any of the upper 32-bit
signals, the two devices could be driving opposite levels. Am i right in
thinking in this direction?
Sol'n: Configure Ur device in output mode(upper 32-bits), when u insert it in 32-bit slots(according to REQ64# logic), drive zero/one onto the upper 32-bit bus.



>>> <Anand.Kuriakose@smartm.com> 07/30/02 11:00PM >>>


Hi,

As per the PCI spec 2.2, sec 3.8.1, the 32-bit PCI extension has to be pulled on
the  motherboard, to prevent them from floating. Heres a situation where the
motherboard has a 32bit PCI bus . There are two on-board 64-bit PCI devices (LAN
and SCSI) on the 32-bit bus. Again, as per the PCI spec 2.2, sec 3.8., we see
that these PCI devices monitors the REQ64# signals during PCI reset de-assertion
to determine the width of the PCI bus. In the above case, these devices will see
that the REQ64# signals is de-asserted during reset de-assertion and hence
conclude that the bus width is only 32-bit. Upon determining that the bus width
is 32-bit, these devices will start driving valid bit patterns on the upper
32-bit extension in order to prevent the bus from floating. So heres the
question.

Should i provide on-board pull-ups on the upper 32-bit extension or just leave
them unconnected?
 I personnaly feel that the 32-bit extension of these individaul devices should
be left unconnected (hoping that the devices will take care of preventing the
bus from floating). The other thing i thought if i provided a common on-board
pull-up for the 32-bit extension of both these devices is that there could be
probable data contention, because at any time and on any of the upper 32-bit
signals, the two devices could be driving opposite levels. Am i right in
thinking in this direction?

Thanks in advance.

Anand.