
IBM32NPCXX1EPABBE66
Preliminary
IBM Processor for Network Resources
pnr261_2io.fm.06
August 14, 2000
NPBUS Interface
Page 23 of 706
PBSDATA
1
Output or
Data
This is the data bit that connects to the external serial EPROM to
read from or write to. It must have a pullup resistor attached and
supports the I
C protocol. The range of supported serial EPROM is
from 256 to 2 KB. After reset, the PNR will start accessing the
optional on-card serial EPROM and do the chip initialization func-
tion. If this pin is pulled down (or no pullup), the PNR will assume
that no serial EPROM is attached and will go try to fetch from a par-
allel EPROM.
PBRNWRT
1
Output
Read or Write
This pin allows the PNR to read from or write to internal registers of
the PHY parts. This signal acts as the write strobe when talking to
PMC-Sierra chips such as the Suni-Lite.
PBRDRDY
1
S/T/S
This pin allows the PNR to read from or write into internal registers
of the PHYs by acting as a data acknowledge signal from the mem-
ory slaves. This signal acts as the read strobe when talking to
PMC-Sierra chips such as the Suni-Lite.
PBDATA(7-0)
8
Input/Output
The PB-Bus is an eight-bit wide bidirectional data bus used to inter-
face the PHYs to the PNR. When a data transfer is not happening,
the lower four bits act as MLED(3-0) - four control pins that, under
register bit control, can drive general status to LED devices. If no
EPROM is connected to the PNR, PBDATA(7) and PBDATA(6)
should have external pullup resistors placed on them.
PBINTRA
1
Input
This input from PHY A is an attention line that, when low, indicates
that one or more unmasked flags are set in the status registers of
PHY 1.
If additional PHY parts are added, they should also dot their inter-
rupt line onto this input.
PBPHYRST
1
Output
Implements the net-
work safety features of
the device
This signal implements the network safety features of the PNR. It is
the ORed value of RESET and all of the status bits cause the PNR
to stop transferring data. It is asserted for a pulse, and then
removed. This signal is asserted low.
Table 8: NPBUS Signal Descriptions
(Continued)
Signal Name
Quantity
Type
Function
Description
S/T/S = a sustained tri-state pin owned and driven by one and only one agent at a time. The agent that drives the S/T/S pin low must
drive it high for at least one clock before letting it float. A new agent cannot start driving a S/T/S signal any sooner that one clock after
the previous owner tri-states it. A pullup is required to sustain the inactive state until another agent drives it and must be provided by the
central resource.