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The keypad and
LED display support
the low-level Machine Monitor program. I never really used it much, but
it's
a lot like the old KIM-1
monitor except with 24-bit addresses. Not visible are two 65C22 VIA's
and some other stuff hidden underneath
the display and the keypad — both of
which plug
in on headers. The display is recycled from an old calculator. The big red button is a Shift key that alters the meaning of the keypad keys. The little red button (intentionally difficult to press) is the main Reset. The RCA jack is the monochrome video out. |
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The 65C02 CPU is in the center here. To the right of it is the VIA that contains the IP register. The W register is visible on the left: it's implemented as two 74HC574's piggy-backed one on top of the other. The white flying leads establish connections to the Clock and Output Enable pins of the upper chip — the only lines not paralleled with the IC underneath. The big card-edge connector is unused. |
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The 28-pin chips are the main memory. Here again we see chips piggy-backed atop one another for higher density. In this case the white flying leads are Chip Selects. Battery backup renders the CMOS static rams nonvolatile. And... (have we died and gone to heaven?) ...there's a quarter of a megabyte there! |
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The two EPROM's
that form the microcode Control
Store are dead center, with their address logic nearby: the '163
counter (right) and '273 instruction
register (left, below). At the top is the crystal for the master oscillator, but missing from its socket next door is the associated hex inverter chip. That socket usually held a little daughter board with a carefully built RC oscillator controlled by a trimpot. It was inelegant, but it was good for testing and it also allowed me to run the master clock at 80 Mhz even though I wasn't able to obtain an 80 Mhz crystal. The 65C02 ran at 1/16 of that rate: 5 Mhz. |
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Looking
from a different angle we see the edge-mounted copper bus bars
that run lengthwise along the board. These and some less conspicuous
conductors form an X-Y grid of connections that crudely approximate a
ground plane,
appropriate for KK's logic (which includes 74AC
series chips running as high as 80 MHz). Every IC's ground pin connects
to a junction on the X-Y ground grid,
and likewise every IC has a bypass capacitor (typically
mounted underneath
the chip in the cavity of the IC socket). |
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