little bat / Develop / Hardware / K1-Computer / K1-CPU / DRegs /
Overview | Control Unit | Microcode Header | Arithmetic Unit | Data Registers | Address Registers | Expansion Bus

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K1 16/16 CPU

Data Registers

Last updated: 2012-05-03
Questions & comments to Kio

The last days i was working on the data registers board. The major problem was, to decide what actually will go on this board and how to wire up the RAM address and data lines. Now it's in a state where i think it is near finished. The ALU baord is still in production, and after that has arrived i will probably order the data registers and the address registers board in one go. The address registers board still had a bug. It's not bad to wait a week or two, so i can think over it all again.



The registers again are very straight forward. Input and output connect to their data line. This is basically the same for the shift and the byte swap registers too, except that the data lines for input and output are different here. The clock lines for some registers are strobed with the system's main clock CLK, because this is done for all registers on the control unit, except for 8 data registers, because i needed the unstrobed clock for I/O and RAM, and the colck lines are decoded in groups of 8 by the 74AC138 3:8 decoders. So i must strobe some of them (at most 6) explicitely on the data registers board.

DRegs 5.B circuit registers.png

DRegs 5.B circuit shift, swap.png

DRegs 5.B circuit AxD, IVAL.png

The RAM circuit was a little bit tricky, because i enable the upper or lower RAMs based on an address line, and the switching must occur for both at the same time, or there will be data collission for some nano seconds. And, again, i added "strong" pull-ups to extend the inactive state slightly, so unavoidabe bus collission while switching (with no time gap) is reduced to a minimum. Let's see how it works.

DRegs 5.B circuit RAM.png


Board after adding one gate delay to CY input of SL and SR

timing.png The CY input to the SR register mostly failed to read a '1'-bit. After scrutinizing the problem, i found out that the CY input goes away simulaneously with the clk signal for the register:

The blue clk is the load signal for the registers and the rising edge is where it latches new data from the data bus and, in case of data bit D15, from the CY line. The CY line is a 'option control' line, it controls options in the various registers, if they have. As can be seen in the image the option control line toggles exactly at the same moment (if it toggles) when the clk line raises.

So i had to delay the CY line. I inserted the unused OR gate from IC21 into the CY line and i hope the problem is now solved.


Name Letzte Änderung Länge 
Images/ 2012-05-03 16:27
component placement.png
size: 786 × 492
2009-11-06 10:15 35427 
DReg 5.C.brd 2009-11-03 18:16 100627 
DReg 5.C.s#1 2010-01-22 15:16 128335 
DReg 5.C.s#2 2009-10-12 13:07 128335 
DReg 5.C.sch 2010-01-28 20:44 128335 
DRegs 5.B circuit AxD, IVAL.png
size: 878 × 620
2009-09-27 15:19 33152 
DRegs 5.B circuit RAM.png
size: 878 × 620
2009-09-27 15:18 29193 
DRegs 5.B circuit registers.png
size: 878 × 620
2009-09-27 15:18 22116 
DRegs 5.B circuit shift, swap.png
size: 878 × 620
2009-09-27 15:18 29045 
part list.txt 2009-10-12 14:05 253 
signal length.txt 2010-01-29 18:13 345 

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