CRAM question

For anything related to VDP (plane, color, sprite, tiles)

Moderators: BigEvilCorporation, Mask of Destiny

Post Reply
Posts: 25
Joined: Wed Jun 30, 2021 7:31 pm
Location: United States Of America

CRAM question

Post by Okie » Sat Sep 11, 2021 5:58 pm

The CRAM is 64 9-bit words. We access the memory as a word in format 0000bbb0ggg0rrr0. When they say it is stored in CRAM as a 9-bit word , does this mean that all the zeros are not there and its just bbbgggrrrbbbgggrrr...etc for 72 bytes? The description of a "word" is what confuses me as it is a length related to the processor like the max size to Registers or Memory. How could the max size you can send through be a power of 2?

TmEE co.(TM)
Very interested
Posts: 2425
Joined: Tue Dec 05, 2006 1:37 pm
Location: Estonia, Rapla City

Re: CRAM question

Post by TmEE co.(TM) » Sun Sep 12, 2021 1:49 am

CRAM is a physical array of 64 x 9 bits on the silicon, the unused bits in the data port are simply not connected to the actual memory at least as far as writes are concerned. These unused bits can be anything, they simply are ignored when writes are done. For reads I am unsure what will happen, are they forced to zero or random stuff... I never tried to do this and determine the results, perhaps someone has and can chime in.

Word is width of the databus or data port etc, which is 16bits. The power of two part is for addresses, and you get 64 usable addresses in the CRAM range, one for every color.
Mida sa loed ? Nagunii aru ei saa ;)
Files of all broken links and images of mine are found here :

Post Reply