22 Mar
2014
22 Mar
'14
3:46 p.m.
Hi folks,
I have or don't have a problem with one of the OmniUSB board. I just don't know.
So is there anybody who has tried to use a board in a pdp8/a? Or is there
someone with a board and a pdp8/a at hands to give it a try?
This is the story: I distributed most of the OmniUSB boards last year. And did
not get very much feedback from the people who bought them. I know only of one
party having successfully used the board. All boards have been checked with a
special CPLD firmware and a checkout program on the pdp8 which together provide
complete test coverage for all signal ways going to the pdp8 and back. Even the
DIP switches were tested individually. So I strongly assume that all boards I
shipped are working fine. But.... A few weeks ago I got informed of a board just
not doing anything in a pdp8/a. I gave hints how to use it etc. Then I asked to
send the board back to me to check what is wrong with it. The board arrived and
I put it into my development 8/e - works perfectly. I also did my checkout
routines - everything seems to be perfectly fine. Now I have no idea what could
be wrong. Something with the 8/a? Or a general 8/a issue? The 8/a has the same
CPU as the 8/e afaik. Could there be some subtle differences between 8/a and /e?
Following some detailed info about how OmniUSB talks to the Omnibus:
These are the signals from and to the Omnibus:
-- Omnibus connections
io_pause : in std_logic;
ts3 : in std_logic;
tp3_n : in std_logic;
sw_n : in std_logic;
initialize_n : in std_logic;
md : in std_logic_vector (3 to 11);
DATA_R : in std_logic_vector(4 to 11);
DATA_D : out std_logic_vector(4 to 11);
internal_io_d : out std_logic;
c0_d : out std_logic;
c1_d : out std_logic;
skip_d : out std_logic;
int_rqst_d : out std_logic;
The most operations are enabled by a signal named io_active which is:
io_active <= io_pause and ts3;
e.g.
if (match_rx = '1' or match_tx =
'1') and io_active = '1' then
internal_io_d <= '1';
end if;
for driving the internal_io Omnibus line
Might this be a problem? Is there anything different with 8/a bus timing? Is the
TS3 signal unavailable? Is the io_pause signal unavailable?
I appreciate any hint.
Kind regards
Philipp