8 Oct
2008
8 Oct
'08
2:29 p.m.
On 08/10/2008 21:27, Tony Duell wrote:
Minor correction. The Acorn teletext adapter, which
used the SAA5020 etc
chipset did, indeed connect via the 1MHz bus. But the (IMHO) nicer Morley
one connected to the User Port.
So it does. I'd forgotten.
It had an I2C interface to an SAA5240
chip (this teletext decoder used the I2C bus mot only to select the page,
etc, but also allowed you to read/write the teletext page memory, so
transfering the page to the BBC micro was relatively easy). There was
also a CITAC (Computer Interface for Tuning and Control) chip on that I2C
bus (I forget which one was used), this was used to select the TV
channel, IIRC the Acorn one had 4 preset pots to select the channel, the
computer could then select one of 4 channels.
Yes, the tuning on the Acorn one is definitely not one of its stronger
points! Apart from only having four presets, which arguably made sense
in the UK in 1982, they're very fiddly to set.
--
Pete Peter Turnbull
Network Manager
University of York