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Apple II Computer Info

Obtaining the Crystal oscillator

The WDC supplied document explains why the oscillator must be four times

the speed that you wish to run your system at. The shmoo plot supplied

with the processor will enable you to identify what speed the processor

can run at.

You then must obtain the appropriate oscillator.

Oscillators are available on this side of the Pacific Ocean from Clarke &

Severn Electronics. Different speed oscillators have different prices

ranging up to $12. Contact them for information as to pricing and

availability. Non "off the shelf" speed oscillators can also be ordered

at a cost of $21 each. The TWGS uses a 1/2 TTL oscillator. The

oscillators supplied by Clarke & Severn are standard size TTL

oscillators. This means you will need to modify the oscillator to fit the

TWGS. The WDC supplied document describes one method of doing this.

Another is to obtain a 16 pin DIP socket from Dick Smith Electronics for

40 cents. Cut 8 pins off of one end, and solder a jumper wire between the

8th pin (cut off) and the 4th pin (not cut off) on each side. This method

has the added advantage of making oscillator swapping an effortless task

whereas the NAUG method involves modifying the actual oscillator.

As an alternative to Clarke & Severn, you may like to try Digi-Key in the

USA. Digi-Key have the following 1/2 TTL oscillators which fit into the

TWGS with no modifications:

Mhz Part Price (US$)

------ ------ -----

32 SE1101 3.60

33.33 SE1102 3.60

36 SE1103 3.60

40 SE1104 3.60

42 SE1105 3.60

46 SE1106 3.60

48 SE1107 3.60

50 SE1108 3.60

55 SE1109 3.60

60 SE1110 3.75

If you wish to look for other alternatives, make sure that you get TTL or

CMOS oscillators. Sizes are 1/2 or standard. They come in metal and

plastic bodies. The plastic ones work just fine and are possibly cheaper.

Obtaining faster cache memory

The standard TWGS 8k cache memory is 45 nanoseconds (ns). The 32k cache

memory is 35ns. 35ns is supposedly fast enough for 14Mhz so you may not

need faster SRAMs than this. Experimentation is still continuing in this

area. SRAMs used by the TWGS and Zip GS are 32768x8 general purpose

SRAMs. Try and get chips needing the lowest power requirements.

Sony make a very low power 25ns chip, CXK58258B-25LL, and a 15ns chip

CXK58258A-15. VLSI Tech make 25ns, 20ns and 15ns chips: VT62832UHL-25,

VT62832UHL-20, VT62832UHL-15. Other 25ns chips are Mosel, MS62256-25, and

Paradigm, PDM41256L-25.

All the chips mentioned are available in 28 pin DIPS, with tri-state

outputs.

Some may only be available in .3 inch or .6 inch widebody packages. My

TWGS 32k Cache upgrade takes the .3 inch packages but you should check

yours to make sure you get the correct size, otherwise some messy

soldering could be involved.

Increasing the Power Supply

Apple II Computer Technical Information : Apple II Family Hardware Info

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