Enhanced Configuration Devices (EPC4, EPC8 & EPC16) Data Sheet
internal interface to the flash. Simultaneous access by the controller and
the external device will cause contention, and result in configuration and
programming failures.
Since the internal flash interface is directly connected to the external flash
interface pins, controller flash access cycles will toggle the external flash
interface pins. The external device must be able to tri-state its flash
interface during these times and ignore transitions on the flash interface
pins.
1
The external flash interface signals cannot be shared between
multiple enhanced configuration devices because this causes
contention during in-system programming and configuration.
During these times, the controller chips inside the enhanced
configuration devices are actively accessing flash memory.
Therefore, enhanced configuration devices do not support
shared flash bus interfaces.
The enhanced configuration device controller chip accesses flash memory
during:
■
■
■
FPGA configuration—reading configuration data from flash
JTAG-based flash programming—storing configuration data in flash
At POR—reading option bits from flash
During these times, the external FPGA/processor must tri-state its
interface to the flash memory. After configuration and programming, the
enhanced configuration device’s controller tri-states the internal interface
and goes into an idle mode. To interrupt a configuration cycle in order to
access the flash via the external flash interface, the external device can
hold the FPGA’s nCONFIGinput low. This keeps the configuration device
in reset by holding the nSTATUS-OEline low, allowing external flash
access.
f
For further details on the software support for the external flash interface
feature, refer to Using Altera Enhanced Configuration Devices, chapter 3 in
volume 2 of the Configuration Handbook. For details on flash commands,
timing, memory organization, and write protection features, refer to the
appropriate flash data sheet (Sharp LHF16306 for EPC16 devices and
Micron MT28F400B3 for EPC4 devices) on the Altera web site at
www.altera.com.
Figure 2–4 shows a FPP configuration schematic with the external flash
interface being used.
Altera Corporation
August 2005
2–13
Configuration Handbook, Volume 2
ALTERA [ ALTERA CORPORATION ]
