Z4648252@SFAUSTIN.BITNET (Z4648252) (10/15/89)
Can anyone shed some light preparing a Mega2 ST that has six ROM
sockets for use with the T16 and upgrading the Mega2's memory to four meg?
I've been reading conflicting data about what brand and speed memory
chips to use if one wants to use the T16. I've also been reading that
the T16 is happier if used with fast ROM, that is, copying the original
TOS 1.4 EPROM into faster EPROM chips.
Also, should the older 'Atari' blitter be replaced with the newer?
Incidentally, the 74LS373 chips have been replaced. I had problems
with Spectre until they were.
SIGH...this is a terribly worded letter. Basically, I'm only
asking:
1. What memory chips should be used for upgrading the ST2 to a ST4
if used with the T16?
2. Should the chipped TOS 1.4 be transferred to fast EPROMS to gain
maximum results from the T16?
3. Should the Atari blitter be replaced with the newer?
4. Yes, the 74LS373 chips have been replaced.
Larry Rymal: |East Texas Atari 68NNNers| <Z4648252@SFAUSTIN.BITNET>hase@netmbx.UUCP (Hartmut Semken) (10/19/89)
In article <891014.11320557.073300@SFA.CP6> Z4648252@SFAUSTIN.BITNET (Z4648252) writes: >1. What memory chips should be used for upgrading the ST2 to a ST4 > if used with the T16? 1-Megabit chips (51 1000, 41 1000) with 120 or 150 nanosecond access time; do not worry about "page mode" or "nibble mode" types: these are special, faster read/write modes for the RAMs, that are not used by the ST MCU. Any type should support the "standard" read/write cycle. The ST timing is made for 150 ns RAMs. Faster RAMs may cause problems: the faster the RAM chip can produce/take data (read/write cycle), the faster it must go from "power down" state (about 30 to 40 Milliwatts) to "power up" state (around 300 Milliwatts). This means, the suppy current has to jump from <8 mA to ~60 mA; this leads to voltage drops on the power lines (the faster the jump, the less power left for the RAM...) The 1985 Rev. C 520 ST+ did not cause a lot of trouble when the capacitators for each RAM were replaced with 200 nanofarads. If You want to "recycle" the RAM chips for a new machine (there *will* be another computer in Your life!), get fast chips (70 nanosecond) and a bag of 200 nF capacitators; solder the capacitators between Vcc and Vss under the RAM socket (on solder side of the PCB); if it does not work, solder a second capacitator to every RAM chip; this gives 400 nF per chip and should be all You need. >2. Should the chipped TOS 1.4 be transferred to fast EPROMS to gain > maximum results from the T16? Well, the fastest bus cycle of the 8 MHz 68000 MPU is about 250 nanoseconds long (do not have the specs at hand, maybe its a little less), so the acces of 250 ns ROM/EPROM does not require "wait states" (think about a loop, that fills all registers from memory; with "no wait" the MPU speed is the limiting factor, not the memory speed). However, the 16 MHz MPU is twice as fast; if the memory can produce/take data at the doubled speed, You'll get no wait states, too. Of course a faster ROM is necassary to handle this speed. 200 ns ROMs/EPROMs will do it with a little trick: the acces time of EPROMS is measured from the activation of -CE (Chip Enable, low active): 250 ns after -CE the data outputs will be valid. You can think of -CE controling a large transistor that switches the power to the chip on and off; disabled, the chip is sleeping (and taking less power, producing less heat), -CE awakes it. Now, there is another control input, called -OE (Output Enable). This one enables the output drivers of the (awake) chip. If the chip is held awake (-CE constant low), the acces time (after activation of -OE) is a lot (!) faster than nominal speed. Its less than half the nominal acces time. The chip is now twice as fast: it can catch up with a MPU, that is twice as fast. The faster adress decoding and timing is - of course - not handeled by the ST chip set. The accelerator board has to provide the new control lines. >3. Should the Atari blitter be replaced with the newer? Hmm. Terra incognita, data input required. :-) hase -- Hartmut Semken, Lupsteiner Weg 67, 1000 Berlin 37 hase@netmbx.UUCP Dennis had stepped up into the top seat whet its founder had died of a lethal overdose of brick wall, taken while under the influence of a Ferrari and a bottle of tequila. (Douglas Adams; the long dark teatime...)