MANUAL - hunter memory board

Discussions about Sinclair ZX80 and ZX81 Hardware
David G
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Joined: Thu Jul 17, 2014 7:58 am
Location: 21 North, 156 West

hunter manual Page 10 3732 EPROMs, RAM/EPROM mixture, EEPROMs

Post by David G »

This documentation is "Issue 5 March 1984" ( index )
Page 10 8K NONVOLATILE MEMORY
============================

MODIFICATIONS FOR 2732 EPROM'S

The same modifications are made if the 2732 EPROM's are to be used. Sockets 1 and 3 are used for two 2732 EPROM's. Jumpers J2 are placed as shown in Figure 3. If you use the board for 2732 EPROM's note that you can fully populate the board with four 2732's (16K) and then switch, or page, between the pair in sockets 6 and 2 and the pair in sockets 1 and 3 (8K each) by switching pin 14 of the 74LS139 decoder from +5V (for sockets 1 and 3) to ground (for sockets 0 and 2). Pin 14 of the 74LS139 can be accessed via the upper left hole in J2.


MODIFICATIONS FOR A RAM/EPROM MIXTURE

HM6116 CMOS RAM's and 2716 EPROM's are pin compatible. You can replace one of the 6116's without circuit modification. For a permanent replacement use jumpers J5 and J6 to supply the full +5V to the EPROM. If J5 and J6 are inserted then both the pin 21 trace and the pin 24 trace must be cut between the 2716 and 6116LP sections. Always have the 2716 EPROM's to the left (lower address) of the 6116LP RAM's. All other traces to the pin 24 of each 2716 socket must also be cut. An example -- one 2716 and three 6116LP devices -- is illustrated in Figure 16. It's also possible to have 2 2716's and 2 6116's. Note that if an EPROM is used then the transistor and its two associated resistors can be omitted for that location as described above.

FIGURE 10 cut pin 24 trace cut pin 21 trace
FIGURE 10.jpg
add jumpers
hunter no changes on circuit side
2716 6116

It is recommended that, at least for experimentation, you use two boards -- one configured for CMOS RAM and the other for EPROM. Both can be connected at the same time so long as a particular socket is occupied on only one of the boards. If you wish to do this then a kit of a second board, a wire-wrap edge-connector, a pc edge connector board, five IC sockets, a 74LS139 decoder, a tantalum capacitor, four ceramic capacitors, and a diode (all you need), may be obtained for the special price of $20 post paid if you return your initial receipt.


MODIFICATIONS FOR EEPROM'S

It is possible to read EEPROM's on the board just like the EPROM's described above. Moreover, with the addition of a device to extend the write-enable signal to 1 or 10 ms (depending on the EEPROM), it is possible to write into the EEPROM. Refer to an article by Joe Blagg in BYTE (February 84 page 342) or to Application note #8 by Danton Leonard of SEEQ TECHNOLOGY, 1849 Fortune Drive, San Jose, CA 95131.
David G
Posts: 387
Joined: Thu Jul 17, 2014 7:58 am
Location: 21 North, 156 West

hunter manual Page 11 SYSTEM RAM USE and 32K+

Post by David G »

This documentation is "Issue 5 March 1984" ( index )
Page 11 8K NONVOLATILE MEMORY
============================

MODIFICATIONS FOR USE AS SYSTEM RAM

When the board is used as system RAM the battery back-up is unnecessary and the same modifications described above for 2716 EPROM's can be made. However, if you intend to vary the use to which you put the board it is advisable to follow the assembly instructions detailed above for assignment to the transparent region. Changing over to system RAM is then done very simply by changing jumper J1 to position 2 and adding jumper J3 as illustrated in Figure 4. Note that cheaper NMOS memory IC's can be used in place of CMOS if the board is to be used as system RAM.


USING THE BOARD IN A SYSTEM WITH MORE THAN 32K

This board, like the Sinclair RAM pack, completely ignores AL5 and is therefore limited to use within a 32K system. The board is enabled through _MREQ_ only. See Figure 13. It is however possible to use the board in a system addressing more than 32K by adding additional decoding. Moreover, it is possible to use the board in any 8K slot in such a system.

If the board is to be used as transparent memory (8-16K) in a system larger than 32K then the following procedure is suggested. In effect, Al5 is combined with _MREQ_ in enabling the 74LS139 decoder. The gate used can be an OR gate, a combination of three NAND gates, or two NOR gates, etc. The following procedure refers to the use of a 74LS32 quad 2-input OR gate.

l. Remove the 74LS139 (1C5) from its socket.

2. Very gently bend up pin 1 and then bend it over sideways:
11a.png
3. Obtain a 74LS32 IC and, again very gently, straighten pins 1 and 2 so that they point directly out. Pin 3 should be bent sideways as shown below. Pins 7 and 14 should be bent sideways a little. With loss of little power (less than 1 mA current), pins 4 through 6 and pins 8 through 13 can be cut off at the body of the IC. Check the following sections in this manual before you cut off any pins.
11b.png
4. Mount the 74LS32 on top of the 74LS139. A thin strip of tape wrapped around their bodies will hold them together while you solder the leads. Pin 1's should be at the same end.
David G
Posts: 387
Joined: Thu Jul 17, 2014 7:58 am
Location: 21 North, 156 West

hunter manual Page 12 WRITE PROTECT SWITCH

Post by David G »

This documentation is "Issue 5 March 1984" ( index )
Page 11 8K NONVOLATILE MEMORY
============================

5. Solder together:

Code: Select all

                         74LS139       74LS32 
(small amount of solder  -------       ------
 and do not overheat)     pin 16   to  pin 14
                          pin  8   to  pin  7
                          pin  1   to  pin  3
solder pin 3 of 74LS32 to pin 1 of 74LS139
12a.jpg
74LS32 on top
solder pin 7 of 74LS32 to pin 8 of 74LS139
attach leads to pins 1 and 2

6. Solder flying leads (about 1" insulated) to pins 1 and 2 of the 74LS32.

7. Reinsert the dual IC package into the original socket on the board.

8. Solder the free ends of the two flying leads to A15 and _MREQ_ at the edge connector. It doesn't matter which lead goes to which connector.

9. The board is now uniquely addressed in the 8K to 16K region and can be used in a 64K system.

In order to use the board as RAM above 32K, it is necessary to gate (AND)
_MI_ with A15 in the decoding of the address. The article by John L. Oliger on
page 5 of number 5 volume 3 (1982) of SYNTAX is recommended. The technique
of mounting another IC on top of the 74LS139 can still be used.


WRITE PROTECT SWITCH

Addition of a write-protect switch to your nonvolatile memory board is worthwhile. It avoids loss of data which occasionally happens upon power-down and it can be used to prevent accidental writing over the memory when you test a machine language routine for the first time. The switch can be epoxied to the front of the NVM board opposite the reset switch.

Replace C3 with a 4.7K resistor from the top hole for C3 and the center hole of J2 as shown in Figure 11. Add the switch between the lower two holes of J2. Open the switch to disable a write operation. Note that you MUST open the switch before power-down or the current from the lithium cell will drain 100 times more quickly (back into the computer!). An alternative is to isolate the line through a transistor or one of the gates in the 74LS32.

FIGURE 11
4.7k resistor added
FIGURE 11.jpg
Switch (open to protect)
David G
Posts: 387
Joined: Thu Jul 17, 2014 7:58 am
Location: 21 North, 156 West

hunter manual Page 13 a. PAGING

Post by David G »

This documentation is "Issue 5 March 1984" ( index )
Page 13 8K NONVOLATILE MEMORY
=============================

PAGING

With the proliferation of devices using the 8-16K region it would be very useful to be able to have all the devices plugged in at one time but to enable only the one you wished to use at a particular instance. In such a system, each device would be addressed by a unique enable signal. This signal may be memory-mapped (the BASIC POKE command may then be used) or it may be generated in the I/O space (the machine language OUT command must be used because the SINCLAIR BASIC has no IN or OUT command). In order not to load down the data, address, and control lines of the ZX81 it is advisable to buffer them. See for example the diagram on page 37 of the Winter 1982 issue of SQ (Syntax Quarterly).

Each peripheral device then should have a device-enable input. One can be made for the 8K nonvolatile memory board using a gate in the 74LS32 quad OR IC as shown in Figure 12. The best way to disable the NVM board is shown in Figure 12. It has the advantage of not interfering with the_ROMCS'_ signal. Jumper J1 is replaced. Several boards can be attached simultaneously using this method.

FIGURE 12
FIGURE 12.jpg

Code: Select all

          |-----------|
       J1 | O O O O O-|---------|
          |---|-------|         |
              |                 |
       enable for 8-16K   _     |
         (active low)---o| \    |
                         |  |o--|
device select input-----o|_/
(active low)         4LS32 OR gate
A manual switch may be substituted for the device select signal and the OR gate -- in this case tie the output of the Switch to +5V via 2 to 5K.
David G
Posts: 387
Joined: Thu Jul 17, 2014 7:58 am
Location: 21 North, 156 West

hunter manual Page 13 b. PARTS LIST

Post by David G »

This documentation is "Issue 5 March 1984" ( index )
Page 13 8K NONVOLATILE MEMORY
============================

PARTS LIST

1 Main pc board
1 Pc board edge connector
1 44 pin wire wrap edge connector
4 24 pin sockets
1 16 pin socket
1 momentary push button switch (Panasonic EVQ-P1R04K)
1 lithium cell holder (Memory Protection Devices BH906)
1 lithium 3V cell (Panasonic BR2325; Sanyo CR2032; etc.)
1 HM6116LP-3 150nsec low power 2K CMOS RAM (IC1)
1 74LS139 decoder (IC5)
3 1N4148 silicon diodes (D1-D2, D4)
1 1N270 germanium diode (D3)
5 NPN general purpose silicon transistors (2N3904) (Q1-Q5)
1 100 ohm resistor (Rl; brown black brown)
4 1K resistors (R2-R5; brown black red)
1 4.7K resistor (for write-protect switch; yellow violet red)
6 10K resistors (R6-R10, R12; brown black orange)
1 100K resistor (Rll; brow black yellow)
1 10uF 16V tantalum capacitor (Cl)
1 0.047uF bypass capacitors (C2-C5)
1 instruction manual
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