[Coco] Byte Order Question
rtaylor at bayou.com
Wed Jul 28 00:42:06 EDT 2004
At 09:35 PM 7/27/2004, you wrote:
| For instance, if I have a 32 bit value of say 0x41424344 ('ABCD') and I
| were to write that to video display memory, what would I see?
This little program reveals exactly what you are asking:
start jsr 43304 clear screen
ldq #$41424344 'ABCD'
ldd #1536-96 move cursor out of the way
First, try to view the CoCo's memory map with $0000 as being at the roof
top of the skyscraper, and $FFFF as being at the basement. The CoCo's
video screen is on the floor right below the rooftop, and it's address
range travels downwards as the addresses increase.
For the CoCo, AB would be case if you stored $4142 into RAM. If you stored
$4142 into address $0000, A($41) would be at address $0000 and B($42) would
be at address $0001. If you stored $41424344 into $0000, the same ordering
would apply. $44 would be at address $0003, the higher address.
HOWEVER, the $44 byte in $41424344 is the LEAST-significant byte and $41 is
the MOST-significant byte. So I think it's safe to say that a register's
least-significant byte will be stored at the higher address in memory (or
closer to the basement/floor).
More information about the Coco