U1AFS600-2FG256YI
| Model | U1AFS600-2FG256YI |
| Description | Field Programmable Gate Array, |
| PDF file | Total 334 pages (File size: 18M) |
| Chip Manufacturer | MICROSEMI |
Fusion Family of Mixed Signal FPGAs
Crystal Oscillator
The Crystal Oscillator (XTLOSC) is source that generates the clock from an external crystal. The output
of XTLOSC CLKOUT signal can be selected as an input to the PLL. Refer to the
for more details. The XTLOSC can operate in normal operations and Standby mode
(RTC is running and 1.5 V is not present).
In normal operation, the internal FPGA_EN signal is '1' as long as 1.5 V is present for VCC. As such,
the internal enable signal, XTL_EN, for Crystal Oscillator is enabled since FPGA_EN is asserted. The
XTL_MODE has the option of using MODE or RTC_MODE, depending on SELMODE.
During Standby, 1.5 V is not available, as such, and FPGA_EN is '0'. SELMODE must be asserted in
order for XTL_EN to be enabled; hence XTL_MODE relies on RTC_MODE. SELMODE and RTC_MODE
must be connected to RTCXTLSEL and RTCXTLMODE from the AB respectively for correct operation
during Standby (refer to the
for a detailed
description).
The Crystal Oscillator can be configured in one of four modes:
•
•
•
•
RC network, 32 KHz to 4 MHz
Low gain, 32 to 200 KHz
Medium gain, 0.20 to 2.0 MHz
High gain, 2.0 to 20.0 MHz
In RC network mode, the XTAL1 pin is connected to an RC circuit, as shown in
The XTAL2 pin should be left floating. The RC value can be chosen based on
for
any desired frequency between 32 KHz and 4 MHz. The RC network mode can also accommodate an
external clock source on XTAL1 instead of an RC circuit.
In Low gain, Medium gain, and High gain, an external crystal component or ceramic resonator can be
added onto XTAL1 and XTAL2, as shown in
In the case where the Crystal
Oscillator block is not used, the XTAL1 pin should be connected to GND and the XTAL2 pin should be left
floating.
XT LOSC
FPGA_EN*
SELMODE
MODE[1:0]
RTC_MODE[1:0]
XT L
0
XTL_MODE*
1
XTL_EN*
C LKOU T
Note:
*Internal signal—does not exist in macro.
Figure 2-17 •
XTLOSC Macro
Revision 3
2- 21
