Televideo 925 character rom dump
allisonportable at gmail.com
Wed Apr 24 19:46:34 CDT 2019
On 04/24/2019 07:55 PM, Guy Dunphy via cctalk wrote:
> At 08:14 AM 24/04/2019 -0700, you wrote:
>> On 4/24/19 5:39 AM, Guy Dunphy wrote:
>>> The keyboard controller is an 8049. Firmware not readable.
>> 8049s aren't protected. they are 2k versions of the 8048
>> and can be read as 8749s
> I did try reading it as an 8749. By 'not readable' I meant it read as all FF.
> Using a Topmax device programmer; a fairly good brand.
> Interestingly when I selected Intel 8749 it actually hung on reading. Repeatably. Never seen that happen before.
> Selecting NEC 8749, it read, but got all FFs.
> Considering there's something odd going on, I was quite relieved to verify the chip still works afterwards.
> I hadn't gone as far as getting out the databooks and checking whether 8049 should be readable.
> I thought they are, but the absense of '8049' type in the chip programmer seemed to suggest otherwise. Unless they
> were 'induced' to leave it out to hinder copying?
> Shall look into it further.
The 8049 is readable just like the 8048 save for 2k device. I worked
for NEC back then and had access to intel parts too.
If you can't read it its your programmers fault, FYI the set up is
nearly the same as 8749 but the voltage for the read
function is lower. Here is except of page 2-19 of the intel MCS48
family manual july 78...
"The processor is placed in the READ mode by applying a high voltage
(+25V for the
8748, +12V for the 8048/8049) to the EA pin and +5V to the TO (8748
only) input pin.
RESET must be at OV when voltage is applied to EA. The address of the
to be read is then applied to the same lines (TTL levels) of BUS and
Port 2 which output
the address during single step (see below), The address is latched by a
"0" to "1"
transition on RESET and a high level on RESET causes the contents of the
memory location addressed to appear on the eight lines of BUS."
It is possible that the devices is being used with external rom/eprom
the test for that is pin7 EA, if EA is high then program access
is external. it was very common to use any 8048/49 in place of 8035/39
in a system and often cheaper due to misprogrammed
parts that can still be used with external rom.
FYI there are no "protection bits".
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