OR2T15B7BA352-DB View Datasheet(PDF) - Lattice Semiconductor
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Description
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OR2T15B7BA352-DB Datasheet PDF : 200 Pages
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ORCA Series 2 FPGAs
Data Sheet
November 2006
FPGA Configuration Modes (continued)
Master Serial Mode
The FPGA DONE is routed to the CE pin. The low on
DONE enables the serial ROMs. At the completion of
configuration, the high on the FPGA's DONE disables
the serial ROM.
In the master serial mode, the FPGA loads the configu- Serial ROMs can also be cascaded to support the con-
ration data from an external serial ROM. The configura-
tion data is either loaded automatically at start-up or on
a PRGM command to reconfigure. The ATT1700 and
ATT1700A Series can be used to configure the FPGA
S in the master serial mode. This provides a simple 4-pin
interface in an 8-pin package. The ATT1736, ATT1765,
and ATT17128 serial ROMs store 32K, 64K, and 128K
E bits, respectively.
Configuration in the master serial mode can be done at
powerup and/or upon a configure command. The sys-
IC tem or the FPGA must activate the serial ROM's
D RESET/OE and CE inputs. At powerup, the FPGA and
serial ROM each contain internal power-on reset cir-
cuitry that allows the FPGA to be configured without
V E the system providing an external signal. The power-on
reset circuitry causes the serial ROM's internal address
E pointer to be reset. After powerup, the FPGA automati-
U cally enters its initialization phase.
The serial ROM/FPGA interface used depends on such
D factors as the availability of a system reset pulse, avail-
IN ability of an intelligent host to generate a configure
command, whether a single serial ROM is used or mul-
tiple serial ROMs are cascaded, whether the serial
T T ROM contains a single or multiple configuration pro-
grams, etc. Because of differing system requirements
and capabilities, a single FPGA/serial ROM interface is
C N generally not appropriate for all applications.
Data is read in the FPGA sequentially from the serial
E ROM. The DATA output from the serial ROM is con-
O nected directly into the DIN input of the FPGA. The
CCLK output from the FPGA is connected to the
L CLOCK input of the serial ROM. During the configura-
E C tion process, CCLK clocks one data bit on each rising
edge.
Since the data and clock are direct connects, the
S IS FPGA/serial ROM design task is to use the system or
FPGA to enable the RESET/OE and CE of the serial
ROM(s). There are several methods for enabling the
D serial ROM’s RESET/OE and CE inputs. The serial
figuration of multiple FPGAs or to load a single FPGA
when configuration data requirements exceed the
capacity of a single serial ROM. After the last bit from
the first serial ROM is read, the serial ROM outputs
CEO low and 3-states the DATA output. The next serial
ROM recognizes the low on CE input and outputs con-
figuration data on the DATA output. After configuration
is complete, the FPGA’s DONE output into CE disables
the serial ROMs.
This FPGA/serial ROM interface is not used in applica-
tions in which a serial ROM stores multiple configura-
tion programs. In these applications, the next
configuration program to be loaded is stored at the
ROM location that follows the last address for the previ-
ous configuration program. The reason the interface in
Figure 41 will not work in this application is that the low
output on the INIT signal would reset the serial ROM
address pointer, causing the first configuration to be
reloaded.
In some applications, there can be contention on the
FPGA's DIN pin. During configuration, DIN receives
configuration data, and after configuration, it is a user
I/O. If there is contention, an early DONE at start-up
(selected in ispLEVER) may correct the problem. An
alternative is to use LDC to drive the serial ROM's CE
pin. In order to reduce noise, it is generally better to run
the master serial configuration at 1.25 MHz (M3 pin
tied high), rather than 10 MHz, if possible.
DATA
CLK
ATT1700A
CE
RESET/OE
CEO
DATA
CLK
ATT1700A
DIN
CCLK
DOUT
TO DAISY-
CHAINED
DEVICES
DONE
INIT
ORCA
SERIES
FPGA
PRGM
ROM's RESET/OE is programmable to function with
CE
M2
RESET active-high and OE active-low or RESET active-
RESET/OE
M1
low and OE active-high.
M0
CEO
In Figure 41, serial ROMs are cascaded to configure
multiple daisy-chained FPGAs. The host generates a
500 ns low pulse into the FPGA's PRGM input. The
FPGA’s INIT input is connected to the serial ROM’s
RESET/OE input, which has been programmed to
function with RESET active-low and OE active-high.
TO MORE
SERIAL ROMs
AS NEEDED
PROGRAM
5-4456.1(F)
Figure 41. Master Serial Configuration Schematic
50
Lattice Semiconductor
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