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参数资料
| 型号： | ATT3042-50S68I |
| 厂商： | Electronic Theatre Controls, Inc. |
| 元件分类： | FPGA |
| 英文描述： | Field-Programmable Gate Arrays |
| 中文描述： | 现场可编程门阵列 |
| 文件页数： | 28/80页 |
| 文件大小： | 528K |
| 代理商： | ATT3042-50S68I |
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Data Sheet
February 1997
ATT3000 Series Field-Programmable Gate Arrays
28
Lucent Technologies Inc.
Special Configuration Functions
(continued)
Reprogram
The FPGA configuration memory can be rewritten
while the device is operating in the user’s system. To
initiate a reprogramming cycle, the dual-function pack-
age pin DONE/
PROG
must be given a high-to-low tran-
sition. To reduce sensitivity to noise, the input signal is
filtered for two cycles of the FPGA’s internal timing gen-
erator. When reprogram begins, the user-programma-
ble I/O output buffers are disabled and high-impedance
pull-ups are provided for the package pins. The device
returns to the clear state and clears the configuration
memory before it prompts
INITIALIZED
. Since this
clear operation uses chip-individual internal timing, the
master might complete the clear operation and then
start configuration before the slave has completed the
clear operation. To avoid this, wire-AND the slave
INIT
pins and use them to force a
RESET
on the master (see
Figure 25). Reprogram control is often implemented by
using an external open-collector driver which pulls
DONE/
PROG
low. Once it recognizes a stable request,
the FPGA will hold a low until the new configuration has
been completed. Even if the reprogram request is
externally held low beyond the configuration period, the
FPGA will begin operation upon completion of configu-
ration.
DONE Pull-Up
DONE/
PROG
is an open-drain I/O pin that indicates the
FPGA is in the operational state. An optional internal
pull-up resistor can be enabled by the user of the devel-
opment system when the bit stream generation pro-
gram is executed. The DONE/
PROG
pins of multiple
FPGAs in a daisy chain may be connected together to
indicate that all are DONE or to direct them all to repro-
gram.
DONE Timing
The timing of the DONE status signal can be controlled
by a selection in the bit stream generation program to
occur a CCLK cycle before, or after, the timing of out-
puts being activated (see Figure 20). This facilitates
control of external functions, such as a PROM enable
or holding a system in a wait-state.
RESET Timing
As with DONE timing, the timing of the release of the
internal RESET can be controlled by a selection in the
bit stream generation program to occur a CCLK cycle
before, or after, the timing of outputs being enabled
(see Figure 20). This reset maintains all user-program-
mable flip-flops and latches in a zero state during con-
figuration.
Crystal Oscillator Division
A selection in the bit stream generation program allows
the user to incorporate a dedicated divide-by-two flip-
flop in the crystal oscillator function. This provides
higher assurance of a symmetrical timing signal.
Although the frequency stability of crystal oscillators is
high, the symmetry of the waveform can be affected by
bias or feedback drive.
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