Post Reply 
Removing FRAM71 Memory Modules?
02-07-2017, 06:15 PM
Post: #2
RE: Removing FRAM71 Memory Modules?
(10-17-2015 03:02 PM)Dave Frederickson Wrote:  What's the best way to remove a FRAM71 memory module from the configuration string?

It sounds like a trivial question and that simply POKEing zeros into the appropriate place in the config string is all that's necessary. This is like pulling out a physical memory module with FREEPORTing it first.

Well, that somehow would give the impression that you could place those zeroes just anywhere in the configuration string, which is not the case. the configuration string must be contiguous. putting zeroes in the middle of the config string masks out the remainder of the config that follows after the zeroes.
for example,
"9394959600.." gives 4 x 32KB RAM, while
"9394009600.." gives only 2 x 32KB RAM, and the RAM at F_Block6 will be ignored.
the reason for that is how HP-71B's config routine interacts with FRAM71's "DIN/DOUT"- handling at power-on: a CHIP in FRAM71 that has its config nibble set to zero is considered to be "not there" (will not respond to an "ID" command) and also will not pass on its "DOUT" dasy-chain signal to the the following chip. thus, the HP-71B doesn't get any further ID response and assumes that there are no more chips to be configured. so, for the above example, the chip formerly known as "95" won't be detected, and chip "96" never gets the "DIN" signal, because "95" doesn't pass it over to "95".
Find all posts by this user
Quote this message in a reply
Post Reply 


Messages In This Thread
RE: Removing FRAM71 Memory Modules? - Hans Brueggemann - 02-07-2017 06:15 PM



User(s) browsing this thread: 1 Guest(s)