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

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K1 16/16 CPU

Address Registers

Last updated: 2010-06-28
Questions & comments to Kio

The address registers board was ordered from LeitOn in October 2009 and arrived and was finished in November.

The address registers board is very straight forward, but of course there is something special too:

AReg 5.8 - circuit registers.png
Address Registers Circuit

AReg 5.8 - circuit adder.png
Address Adder Circuit

The address registers output their data to the address bus which is connected to the address lines of the built-in RAM of the CPU. Their inputs are connected to the address adder. They can only be loaded through the address adder, applying a non-zero address offset, except if they are loaded from the data bus across the data/address bus bridge, where the offset can be zero. The address adder can apply ±1 increment/decrement, +IVAL and +IVAL+$FF00, where IVAL is the low byte from the current instruction code. The up to 4 (6) possible operations are selectable by two option control lines from the control unit (and the state of the bus bridge output enable).

The address adder is a compromise between the wish to be able to add 8 bit displacements and the need for speed. If i had implemented 'my' pure ±1 increment adder, i would have saved ~ 2 gate delays (10ns in 74AC…) and this will probably have an impact on the maximum clock speed of about 20%.

2009-11-03: Board arrived from LeitOn. Gold finish. :-) Bent. :-|

The serpentines are calculated to get roughly the same path lengths for the output enable control lines. On a FR4 board (which is what most PCBs are made from) the propagation speed of a signal is ~ 15cm/nsec, so a length deviation of 15 cm results in a signal delay of 1 ns. The 74AC… gates are switching within roughly 2 ns and have a propagation delay of typically 5 ns, so not too much effort is really needed here. After all this CPU will run at 16 MHz and not 3 GHz. :-) I just want to do my best for the output enable lines, because there is NO delay between switching them, just some meager efforts in pulse shaping for the control lines: the pull-up resistors on the control unit.


Name Letzte Änderung Länge 
Images/ 2019-08-20 05:21
AReg 5.8 - circuit adder.png
size: 858 × 580
2009-09-21 21:49 43417 
AReg 5.8 - circuit registers.png
size: 857 × 406
2009-09-21 14:12 34294 
AReg 5.B.brd 2009-11-03 18:16 89611 
AReg 5.B.s#1 2010-01-22 15:15 111287 
AReg 5.B.s#2 2009-10-12 14:26 111287 
AReg 5.B.sch 2010-01-28 20:43 111287 
component placement.png
size: 786 × 492
2009-11-06 10:10 30813 
part list.txt 2009-10-12 14:31 227 
signal length.txt 2010-01-30 18:08 223 

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