How do I use the external memory interface correctly on the DK-S7G2 kit?
One thing to be aware of is that the external memory interface multiplexes some pins based on the switch settings. These switches allow multiple functions to share the IOs but can limit what functions can be enabled simultaneously. For example, if the enable switch S5 is set to 'ON' for the SDRAM and 'ON' for the External Bus the SDRAM signal lines become much longer and this creates long stub lines to the SDRAM which can cause reflections and signal corruption. If you are getting unreliable SDRAM operation review your use of the expansion bus settings. The Users Manual is referenced below and the key configuration section follows:
The on-board SDRAM connections are shared with Pmod Compatible connectors Pmod C and Pmod D. To use the
SDRAM, set the DIP switches to disable the Pmod C and Pmod D connections and enable the SDRAM connections:
1) Set DIP switch 7 (EXP) on S5 to OFF.
When switch 7 of S5 is OFF, the SDRAM signals are disconnected from the Breakout Board, where the SDRAM
connections are shared with Pmod C and Pmod D.
2) Enable SDRAM by one of the following methods:
• Set DIP switch 1 (SDRAM) on S5 to ON.
• If DIP switch 1 on S5 is in the OFF position, SDRAM can be enabled under software control through the
IIC-controlled I/O Expander U22.
The SDRAM device (U26) connects to the 16-bit data and address bus lines and control signals of the external memory
peripheral on the S7G2 microcontroller. The address, data, and control data signals are connected to the microcontroller
through two separate buffers (U11 and U12) controlled by DIP switch 1 on S5 (SDRAM).
To measure the propagation delay of the SDRAM signals across buffer U11, use test point TP6 located on the SDRAM
side of buffer U11. The signal delay can be probed between breakout pin P6_11 on the breakout pin connector J7 and TP6.