Using PORTD & External ram

[jim]

I have a PIC16F877 and I connected an external parallel ram to it.
PORTD is my data bus.

my question: is it ok to keep changing the port from an in to an out every time I want to read / get the data ?

what I do now is make the port an output using "set_tris_d(0x00);"
then I write data to ram.

then when I want to read it I make the port an input "set_tris_d(0xFF);" and then read the data.

am I doing this right ? or have I totally missed something.

Thanks, Jim
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This message was ported from CCS's old forum
Original Post ID: 126

[Doug Kennedy]

:=I have a PIC16F877 and I connected an external parallel ram to it.
:=PORTD is my data bus.
:=
:=my question: is it ok to keep changing the port from an in to an out every time I want to read / get the data ?
:=
:=what I do now is make the port an output using "set_tris_d(0x00);"
:=then I write data to ram.
:=
:=then when I want to read it I make the port an input "set_tris_d(0xFF);" and then read the data.
:=
:=am I doing this right ? or have I totally missed something.
:=
:=Thanks, Jim
Yes this works fine for me aslong as the read write memory line is syncd
( you don't want to read while you are writing thus having the SRAM and portd fighting each other )
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This message was ported from CCS's old forum
Original Post ID: 127

[John P]

:=I have a PIC16F877 and I connected an external parallel ram to it.
:=PORTD is my data bus.
:=
:=my question: is it ok to keep changing the port from an in to an out every time I want to read / get the data ?

Yeah, I've done this, also using PORTD. I used two 74HC374 octal buffers to store first the low, then the high, address bytes, then to write I put the data on PORTD and activate an additional strobe to load it to the RAM. To read, turn the port into inputs and hit a strobe to activate the RAM's -OE line. So you need the 8-bit port and 4 additional control lines (strobe addr high, strobe addr low, read and write). It's cumbersome, but it does work.

I also took the outputs from the octal buffers and connected each one to an LED. The address lines have no effect when the RAM isn't read or written, so I do a "dummy operation" which sets the address bits but doesn't read or write. By doing this at a suitable rate I've set up a "bouncing light" which goes up and down the row of LEDs twice a second or so. It's fun and it also verifies that every address bit is functioning and that the processor's timing interrupt is working.
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This message was ported from CCS's old forum
Original Post ID: 139

[Robert]

Could you please tell me what RAM chip you use?