Rainbow Electronics AT17F080 - Manual (Page 7)

7
AT17F040/080
3039C–CNFG–11/02
FPGA Master Serial
Mode Summary
The I/O and logic functions of any SRAM-based FPGA are established by a configura-
tion program. The program is loaded either automatically upon power-up, or on
command, depending on the state of the FPGA mode pins. In Master mode, the FPGA
automatically loads the configuration program from an external memory. The AT17F
Serial Configuration PROM has been designed for compatibility with the Master Serial
mode.
This document discusses the Atmel AT40K, AT40KAL and AT94KAL applications as
well as Xilinx applications.
Control of
Configuration
Most connections between the FPGA device and the AT17F Serial Configurator PROM
are simple and self-explanatory.
• The DATA output of the AT17F Series Configurator drives DIN of the FPGA devices.
• The master FPGA CCLK output drives the CLK input of the AT17F Series
Configurator.
• The CEO output of any AT17F Series Configurator drives the CE input of the next
Configurator in a cascade chain of configurator devices.
• SER_EN must be connected to V
CC
(except during ISP).
• The READY pin is available as an open-collector indicator of the device’s reset
status; it is driven Low while the device is in its power-on reset cycle and released
(tri-stated) when the cycle is complete.
• PAGE_EN must be held Low if download paging is not desired. The PAGESEL[1:0]
inputs must be tied off High or Low. If paging is desired, PAGE_EN must be High
and the PAGESEL pins must be set to High or Low such that the desired page is
selected, see Table 2 on page 5.
Cascading Serial
Configuration
Devices
For multiple FPGAs configured as a daisy-chain, or for FPGAs requiring larger configu-
ration memories, cascaded configurators provide additional memory.
After the last bit from the first configurator is read, the clock signal to the configurator
asserts its CEO output Low and disables its DATA line driver. The second configurator
recognizes the Low level on its CE input and enables its DATA output.
After configuration is complete, the address counters of all cascaded configurators are
reset if the RESET/OE on each configurator is driven to its active (Low) level.
If the address counters are not to be reset upon completion, then the RESET/OE input
can be tied to its inactive (High) level.
Programming Mode
The programming mode is entered by bringing SER_EN Low. In this mode the chip can
be programmed by the 2-wire serial bus. The programming is done at V
CC
supply only.
Programming super voltages are generated inside the chip. The AT17F parts are
read/write at 3.3V nominal. Refer to the AT17F Configuration application note available
on the Atmel web site (www.atmel.com) for more programming details.
Standby Mode
The AT17F Series Configurators enter a low-power standby mode whenever CE is
asserted High. In this mode, the AT17F Configurator consumes less than 50 µA of cur-
rent at 3.3V. The output remains in a high-impedance state regardless of the state of the
OE input.