Declaring variables
ok, this might be a silly question. But, how do we declare a "variable" or something that has a name, and we can store values into it later on?
Recently at the beginning of the sample code, I've seen:
1. test 0x70
2. udata_shr
test res 1
3. test equ 0x20
4. #define RS PORTD, 2
5. cblock 0x70
lcd_tmp
lcd_d1
lcd_d2
endc
So these are super confusing... can someone briefly describe what they mean? And which one is for declaring a variable (with or without initial value)?
Thx a lot!
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Replies to This Discussion
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Permalink Reply by Kenny Kim on
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you can't really declare a variable, or at least if you can I'm not sure how but you can declare a register and you but it in the clock section. also you can make your own name for the I/0 ports which is what the # define is for. In your example about you're calling the 2nd I/O pin of PORTD "RS" aka you're making the two labels interchangeable.
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the "equ" directive does pretty much the same thing as define except its a little more finicky. so ur basically saying "goto test" means goto address 0x70. finally I dunno about data_shr although I think Ryan posted about it below so maybe take a look at that?
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of note is that all the things you listed are compiler commands, not assembly code. I'll try and explain all the ones I'm familiar with. udata_shr is meant for multiple file codes (I THINK), but the way it works is it reserves (res) n bytes of memory from the shared general purpose registers (at the bottom at every bank). That specific line section you listed there would have reserved 1 byte of memory for test at 0x70. had there been another line, given that you only reserved one byte of memory, it would have started at 0x71
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cblock 0x70 works in a similar way - putting the 0x70 beside it means you start at the registers common to the bank. It will associate one byte of memory for lcd_tmp at 0x70, one by for lcd_d1 at 0x71, etc.. its use is for when you have a large block of registers that you want to keep for yourself, essentially.
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