
ZestSC1 User Guide
CONFIDENTIAL Page 17 of 57
Figure 6. Register read and write accesses
7.1.1.4 User Signals
The 8 user signals between the FPGA and FX2 can be used for any application defined
purpose. However, care must be taken to set the direction of the FX2 Port C signals such
that the FX2 and FPGA do not drive against each other at any time. Failure to do so may
result in damage to the hardware.
7.1.1.5 Host Interrupt
The user core exposes a single signal to interrupt the host.
User_Interrupt : in std_logic;
Or, in Verilog:
input User_Interrupt
Setting User_Interrupt high for a single cycle will cause an interrupt on the host which
can be trapped by the user application (ZestSC1WaitForInterrupt() function).
7.2 FPGA
The FPGA is from the Xilinx Spartan-3 family and is either the XC3S1000-4 or XC3S400-
4, according to which was ordered. The package is the FT256 256-pin fine pitch thin BGA.
There are three main devices attached to the FPGA:
• USB controller
• SRAM – 512K x 18 or 4M x 18 of synchronous SRAM
USER CL
USER Re
Addr
USER Re
WE
A0
USER Re
DataIn
A1
USER Re
DataOut
USER Re
RE
D0
D1
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