What is the required RAM architecture for 256Mb chips to be used with ADV7800? Is it 16M16? Also, do you happen to have evaluation board schematics & layout for this chip? Thanks!
This support files can be found here:
Chapter 12 of the hardware manual specifies the memory requirements
Let me know if you need more information
The datasheet only discusses 128Mb memory chips, not 256Mb. I just wanted to double check whether 16M16 RAM is going to work. Documentation for some other chips (like ADV7842) includes PCB layouts for the evaluation boards. I was just wondering whether the same is available for ADV7800.
The hardware manual (from above link) shows the routing. I've attached a schematic with the connections to a 128MB or 256MB parts. Just make sure R112 is populated to tie off A12 if your using the 256MB part.
But if you tie off the A12 address pin, the ADV7802 can then only use half of the 256Mb memory, or am I'm missing something? Looking at the Hardware reference manual on page 234, for register: DEFMCRO[19:18] SDRAM size, one can see that it would be possible to choose a 256Mb memory.
So what changes if you choose 256Mb instead of 128Mb in the DEFMCRO[19:18] SDRAM size register?
And if one look at a 256Mb DDR2 memory which is x16 wide you can see that it needs 13 address pins to be able to address the whole 256Mb memory.
128MB SDRAM requires A0-A11, 256MB requires A0-A12. The ADV7802 only needs 64Mb of memory to store the field. Since the ADV7802 does not have a A12 address pin the A12 pin on the 256Mb part needs to be tied off so it doesn't wiggle causing bad data accesses.
DEFMCRO may change the way column addressing is defined. It's slightly different for each memory size.
You can use a 256Mb memory in a 64Mb slot if you design it right. If you use a x16 memory, the 7802 only needs x8, the unused 8 data bits should be tied off. Also the high address lines should be tied off. For SDRAM A0-A9 contain the mode register definitions during that command so these address lines will be the same for all parts used.
If one check table 51 on page 231 in the Hardware Reference Manual, it describes which functions require which memory. Almost all functions is supported with a 128Mb DDR memory, it is only one function that demands a 256Mb DDR memory (TBC Only, NTSC).
But when the ADV7802 only can address 128Mb of data, there seems to be something wrong in the documentation regarding the above statement of 256Mb DDR?
So if I get this right, there is no point to use anything larger than a 128Mb DDR memory with the ADV7802?
To do Comb+DNR+TBC only requires 128Mb of memory. The 256Mb of memory option is just there to give another possible build option. 128Mb memories are getting harder to get and more costly then 256Mb parts. Price/availability need to be examined at design time to see what's best for you. We just provide the option.
Then I understand, thanks for the help!!
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