Pin Sharing Between Stamp Peripherals

dre

·For a Controller/Datalogger project I am working on I have allotted the following Stamp I/O assignments:

·TLC2543 ADC -··cs, ·Sdo *, Sdi *, clk *

·DS1302 RTC - Data_I/O, Clock, Chip Select

·#27937 Memory Stick Datalogger - RTS, RXD, TXD, CTS#

·For a total allocation of 11 pins. I need to have 7 or 8 pins for control. And the Stamps I have are all the 16 I/O pin version. Hence· the··problem.· Per Tracy's write-up these [noparse][[/noparse]*] pins "can be shared with other serial peripherals". But with which other peripheral pin assignments ?

·If necessary I could use the following IC for control, but I would like to be able to use the "OutH" command for the control pins; and, if possible, I would like to have a few extra pins - as this is a work-in-progress:

·74HC595 shift register -··clk,·Data_in,·Latch

·Any suggestions in regard to pin sharing would be appreciated.

·By-the-way, can I use aliases for shared pin callout?

·cheers, David

Zoot

pin x = TLC2543 Sdo, DS1302 Data_I/O, Memory Stick Datalogger TXD (note: use 1k resistor on bidirectional i/o -- but I thought the 1302 had separate DI/DO/CLK pins? Can't remember...)
pin y = TLC2543 Sdi, Memory Stick Datalogger RXD, 74HC595 data_in
pin z = TLC2543 clk, DS302 Clock, 74HC595 clk

pin a = TLC2543 cs
pin b = DS1302 Chip Select
pin c = 75HC595 Latch
pin d = Memory Stick Datalogger RTS
pin e = Memory Stick Datalogger CTS

Basically any DO/TX lines can be shared, any DI/RX lines can be shared, bi-directional DI/DO can be shared if you have a resistor on the output pin of the peripheral to prevent short when the line is being used as a DI elsewhere. Clocks can always be shared. Chip select (CS, enables, latches, etc) usually need their own pin (although I often use a "master" 74HC595 to control multiple cs/enable/latch lines on peripherals, but the cascading and programming gets a bit thorny).

I'm not familiar enough with the datalogger to be able to say if RTS and CTS can or can not be shared with other lines; if that is possible pin count could be cut by 1 or 2.

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Mike Green

The only pins you could share:

TLC2543 clk with DS1302 Clock

TLC2543 Sdi with DS1302 Data_I/O

You could also use a BS2p40 which has another 16 I/O pins (two banks of 16).

dre

Zoot, Mike,
Many thanks for your replies. I am now confused on a much higher plain . I am going
to first try the design w/o using the -595. I also appreciate the alert on using the 10k
protection resistors.
The reason for not going to the 40 pin Stamp is that I have several regular Stamps
available and I knew that my pin allocation problem could be solved, if necessary, by
incorporating the -595.

Again, thanks, David

Mike Green

The main advantage in using the BS2p40 is that it's much faster using the extra pins because you only need to do a MAINIO or AUXIO to switch between them and you can use all of the existing Stamp statements directly on the bank of I/O pins. With 74HC595s or 74HC165s, you have to shift the data out/in to the chips and that's relatively slow. It works fine for lighting LEDs or sampling switches where a couple of hundred samples per second are ok, but not for anything requiring tighter timing.

tronsnavy

Dre,

Not sure if this would work for your situation but what about decoders/demultiplexers such as the 74LS138. With this IC, you can take 3 i/o pins and make 8 output pins. Each binary value (from 000 to 111) selects one of eight outputs. You said that you need 7 or 8 pins for control. This might work. Check out the data sheet for these IC's. I use them whenever I don't have enough output pins. Good luck.

Bob