512->128

for those who missed it...

published in Adventurer magazine #12 issue

(c) J7n/4D'99

and lastly, one more cartoon -
"#FD protection". Probably many, having expanded the Pentagon512 memory,
often, scolding the coders, click the ON/OFF switch. And all because
it is now fashionable to refer to #7ffd by
#fd, but with mask #40 (all thanks to
Scorps with Kais and their system port
#1ffd). Example: LD a,#50:OUT (#FD),A -
turn on bank 0. Accordingly, someone with
256/512kb starts to turn on the wrong
banks, the ramdisk gets spoiled and other nonsense.
And some even specifically (this is completely in vain) switches the memory using #fd
(Ultrasonic - digital tracker). In short
in short, this problem has been solved a long time ago (I
haven’t used the pent512
on/off switch for a year and a half).

Usually the expansion scheme looks like this:

pent512 on/off
/ ┌─┬─┬─┐
┌───────/ +5V o──███─┘ ┌──────────/C│ │ │
10K │ D6 ├─┤ │ │
WR7ffd │ D7 ┌─┤1│ │1├──
────┘ │ │ │ │
└─┴─┴─┘

A trigger microcircuit is usually a pair
of elements TM2 or TM9 or TM8. TM2
inputsR (must be connected) - 1 and
13, for TM8 and TM9 - 1. Inputs C for TM2
(must be connected) - 3 and 11, for TM8
and TM9 - 9.

Modification scheme:

D7: 1533ЛЭ1

pent512 on/off
/ ┌─┬─┬─┐
┌───────/ └───┬───┬────────oR│T│ │
│ │ │ ├─┤ │ │
┴ +5V o──███─┘ ┌──────────/C│ │ │
10K │ │ D6 ├─┤ │ │
WR7ffd │ │ ──────┤0│ │0├──
────────┬─────────┘ │ D7 ┌─┤1│ │1├──
│ D7.3 │ ────┘ │ │ │ │
│ ┌──┐ │ └─┴─┴─┘
├─8┤1 │ └─────────────────┐
│ │ o10─┐ D7.2 D7.1 │
└─9┤ │ │ ┌──┐ ┌──┐ │
└──┘ └─6┤1 │ ┌3┤1 │ │
A13 │ o4─┤ │ o1─┤<├┘
────────────────────5┤ │ └2┤ │
└──┘ └──┘

Instead of D7, you can use
an inverter and element LL1 (if there are
free ones on the board). Particular attention
should be paid to signal WR7ffd. Here
is an option suitable for Pentagon
and Pros: when there is no entry to the port
WR7ffd=log.0, if yours is different, then
send WR7ffd without inversion (without
D7.3). The operating principle is as follows:
1. LD BC,#7FFD:LD A,#50:OUT (C),A
addressing is complete - A13=bit5,B=1 - at
output D7.1 we have logic 1, the trigger is not
reset,#50 bank is turned on.
2. LD A,#50:OUT (C),A
addressing is short - A13=bit5,A=0
(let me remind you that the 5th bit of A is a lock
#7ffd, so it is always equal to 0)
When WR7ffd=1 is written, then
at the output D7.1 - log.0, which
resets the trigger - 6th and 7th bits. In this way, bank 0 is turned on.

disadvantages: still does not work
UFO 2, because there a #c0 mask is applied before writing to
#7ffd.

p.s. I recently came across the bourgeoisie Subliminal Extasy #3,
plows normally (doesn’t freeze), only there are no sprites in the articles :).
I had to lock the toggle switch:(.

p.p.s. if you have pent1024, then you can access the upper 512k using #fd
(with mask #30)

cYa, J7n/4D.