10 Nov
2005
10 Nov
'05
1:30 p.m.
Tony Duell wrote:
Here's a small typo, the frame buffer is located in block 1 (PPU memory).
Maybe you're right. In fact, although (according to the boardswapper)
the 98780 and the 98770 have slightly different overall video timings,
both use one single scan raster for alpha & graphics with just different
viewable areas. This is not the case for the standard mono crt. So maybe
the parallel operation of alpha & graphics works for the 98780, too. The
color crt enables both displays during initialization (CONTROL+STOP,
thats what the INIT signal is for) and afterwards switches back to
normal alpha only. Maybe the 98780 behaves in a similar manner.
However, I think I got all I need in order to make a first try for some
substitute for the startup fixture. See how it works :-)
--Ansgar
Here it is
with relation to the boardswapper guides:
NP/=MonAck/ --( )-- WrFull/=FLB/
NW/=MonStb --( )-- DD15=GS
Gnd --( )-- MonClrAddr/=NL/
Gnd --( )-- +5V
I6=MD(6) --( )-- +5V
CS=MD(7) --( )-- +5V
I4=MD(4) --( ) N/C
I5=MD(5) --( )-- -Vm
I2=MD(2) --( )-- -Vm
I3=MD(3) --( )-- +Vm
I0=MD(0) --( )-- +Vm
I1=MD(1) --( )-- Gnd
IV=MD(9) --( )-- Gnd
CUR=MD(8) --( )-- MD(12)=RDA
UL=MD(11) --( )-- MD(13)=GRA
B=MD(10) --( )-- MD(14)=BLA
AS=GS/=DA14 --( )-- Gnd
Gnd --( )-- Init/
where
NP = New Page (=> load start address + AS + GS from block 0 at address
600000 into address register
)
NL = New Line
(=> read one line from crt buffer into line buffer)
NW = New Word (=> provide next character+attribute data to monitor)
Well, my names were'd too ridiculous, then, considering I worked them out
before seeing the boardswapper guide.
AS = Alpha Select (=> enable alpha display,
used as GS/ for switching
between alpha and graphics on the monochromes)
GS = Graphics Select (=> enable graphics display on the 9845C only,
where alpha & graphics can be displayed simultaneously)
Are you sure that doesn't also apply to the 98780 enhanced mono monitor?
The text and graphic systems are pretty much seperate on that monitor,
OK, there is one video timing chain (on the text PCB) that provides
timing signals to the graphics board too, but the graphics unit has its
own memory, video shift register, etc. The outputs are combinded by a
fairly complex mixer circuit on the interface PCB in the monitor. There
is no good reason why the 2 can't be displayed at the same time.