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How do I connect external hardware to a LogicTile Express V2F-1XV5 board? Can I stack other boards on top of a LogicTile?

Applies to: Versatile Express Logic Tiles

Scenario

The LogicTile Express V2F-1XV5 board allows the developer to add custom peripheral logic to the Versatile Express development system. FPGA boards belonging to previous families of ARM development systems (i.e. Integrator "Logic Modules" and Versatile "Logic Tiles") supported stacking of these boards to increase the effective FPGA count. The upper header connectors on those boards also allowed connection of ARM-provided or custom-made interface boards to the system. Some users wish to do the same with the Versatile Express system.

Answer

The V2F-1XV5 board does not have system bus header connectors on its top surface. As such, it does not support stacking of further LogicTiles on top of itself, nor can a custom-made interface board be stacked on top.

It is possible however, to build a custom board or cable that connects to the PISMO2 connector on the LogicTile Express. This is a Samtec SEAF-40-06.5-SM-8-2-A-K connector, which is largely populated with direct connections to the LT FPGA. It was intended to be used for connecting small memory expansion boards to the system via the LT FPGA, but there is nothing to stop the developer using it instead for general FPGA I/O connectivity to external hardware.

In addition to various power rails, the PISMO2 connector provides the following single-ended logic signal connections to the tile FPGA:

Table of available FPGA I/O connections on PISMO2 connector
# of pins Signal name groups Associated power rail Notes
9 AUX* 3V3
73 DM* DDR_VIO
3 DM* VIO Output only
126 SM*, NA*, FS* STAT_VIO

In total, this gives the developer access to a maximum of 211 uncommitted FPGA I/O signals for interfacing with external hardware. The exact pinout for the PISMO2 connector is given an another FAQ: What is the pinout for the PISMO2, SATA and HSSTP connectors on the LogicTile? A few of the I/O signals listed above are connected with series termination resistors, or have pullups to a supply rail. This information is given in the full pinout table.

The mating Samtec connector and a custom interface board would need to be built to make use of these connections. ARM does not provide a generic interface board or mating connector for the PISMO2 interface.

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