First thing is that the 'w' and 'x' commands default to 32 bit writes and reads if you don't specify what size you want.

x /w 0x200c0000 = 32 bit read
x 0x200c0000 = 32 bit read
x /h 0x200c0000 = 16 bit read
x /b 0x200c0000 = 8 bit read

This memory area is a 32 bit interface. You may want to check the address you are using also, you only have 7 'hex' digits, should be 8.

So, each address has 32 bits and counts like this:

0x200c0000
0x200c0004
0x200c0008
0x200c000C
0x200c0010
0x200c0014
....
....

If you wanted to write to the two addresses, you can simply use:
w /w 0x200c0000 0x00000000
w /w 0x200c0004 0x00000000

You can also do 16 and 8 bit reads and writes. For example:
w /b 0x200c0004 0xA6

In newer versions of LogicLoader (starting in 1.4) we included a 'mem-fill' command. I don't think this was in a release for the LH79520 though. We have not released newer versions of LogicLoader on the LH79520 since 1.2.6.
This is how mem-fill operates:
mem-fill 0x200c0000 0x8 0x00000000 /w
(this would fill 8 addresses with 0x00000000)

If you needed to write a bunch of stuff into RAM (like an application) you would want to create a .elf file for example and load it into your RAM memory space using the 'load elf' command.

Regards,
-Mike