R
Functional Description
This addressing flexibility allows the FPGA to share the par-
allel Flash PROM with an external or embedded processor.
Depending on the specific processor architecture, the pro-
cessor boots either from the top or bottom of memory. The
FPGA is flexible and boots from the opposite end of mem-
ory from the processor. Only the processor or the FPGA can
boot at any given time. The FPGA can configure first, hold-
ing the processor in reset or the processor can boot first,
asserting the FPGA’s PROG_B pin.
The RDWR_B and CSI_B must be Low throughout the con-
figuration process. After configuration, these pins also
become user I/O.
In a single-FPGA application, the FPGA’s CSO_B and
CCLK pins are not used but are actively driving during the
configuration process. The BUSY pin is not used but also
actively drives during configuration and is available as a
user I/O after configuration.
After configuration, all of the interface pins except DONE
and PROG_B are available as user I/Os. Furthermore, the
bidirectional SelectMAP configuration peripheral interface
(see Slave Parallel Mode) is available after configuration.
To continue using SelectMAP mode, set the Persist bit-
stream generator option to Yes. An external host can then
read and verify configuration data.
The mode select pins, M[2:0], are sampled when the
FPGA’s INIT_B output goes High and must be at defined
logic levels during this time. After configuration, when the
FPGA’s DONE output goes High, the mode pins are avail-
able as full-featured user-I/O pins.
Similarly, the FPGA’s HSWAP pin must be Low to
P
enable pull-up resistors on all user-I/O pins or High to dis-
able the pull-up resistors. The HSWAP control must remain
at a constant logic level throughout FPGA configuration.
After configuration, when the FPGA’s DONE output goes
High, the HSWAP pin is available as full-featured user-I/O
pin and is powered by the VCCO_0 supply.
The Persist option will maintain A20-A23 as configuration
pins although they are not used in SelectMAP mode.
Table 59: Byte-Wide Peripheral Interface (BPI) Connections
Pin Name
FPGA Direction
Description
During Configuration
After Configuration
User I/O
Input
User I/O Pull-Up Control. When
Drive at valid logic level
HSWAP
Low during configuration, enables throughout configuration.
pull-up resistors in all I/O pins to
P
respective I/O bank VCCO input.
0: Pull-ups during configuration
1: No pull-ups
M[2:0]
Input
Mode Select. Selects the FPGA
configuration mode. See Design
Considerations for the HSWAP,
M[2:0], and VS[2:0] Pins.
M2 = 0, M1 = 1. Set M0 = 0 to
start at address 0, increment
addresses. Set M0 = 1 to start at
address 0xFFFFFF and
User I/O
A
decrement addresses. Sampled
when INIT_B goes High.
CSI_B
Input
Input
Chip Select Input. Active Low.
Must be Low throughout
configuration.
User I/O. If bitstream
option Persist=Yes,
becomes part of
SelectMap parallel
peripheral interface.
RDWR_B
LDC0
Read/Write Control. Active Low
write enable. Read functionality
typically only used after
configuration, if bitstream option
Persist=Yes.
Must be Low throughout
configuration.
User I/O. If bitstream
option Persist=Yes,
becomes part of
SelectMap parallel
peripheral interface.
Output
PROM Chip Enable
Connect to PROM chip-select
input (CE#). FPGA drives this
signal Low throughout
configuration.
User I/O. If the FPGA does
not access the PROM after
configuration, drive this pin
High to deselect the
PROM. A[23:0], D[7:0],
LDC[2:1], and HDC then
become available as user
I/O.
DS312-2 (v3.8) August 26, 2009
www.xilinx.com
87
Product Specification
XILINX [ XILINX, INC ]
