8051 Controller

Hello

I am new to the 8051 compatible controller. I am used to PIC as well as 
Renesas and using C.
The 8051 does not have a "Port Direction" to set. I have some questions 
regarding this:

- How to set it as input? I read something of writing 1 to the latch. 
However, this is as using it as output and set it. I don't get its function.
- How to set it as output correctly?
- There is a difference between reading the "pin" and reading "latch". Can I 
somehow select which one I want to read?

Thanks for your help
Franz

<@> wrote:
> Hello
>
> I am new to the 8051 compatible controller. I am used to PIC as well as
> Renesas and using C.
> The 8051 does not have a "Port Direction" to set. I have some questions
> regarding this:
>
> - How to set it as input? I read something of writing 1 to the latch.
> However, this is as using it as output and set it. I don't get its function.
> - How to set it as output correctly?
> - There is a difference between reading the "pin" and reading "latch". Can I
> somehow select which one I want to read?

The 8051 port pins have weak pull-ups, which means if you set them to
'1', you can use them as inputs. There is nothing else you can or must
do to use a pin as an input.
You can't read back the latch AFAIK.

If you want to use it as a an output, you don't need to do anything
either, unless you need more drive on the high side, in which case you
add a pull-up resistor or a buffer.

This is why doing open collector type routines like I2C, one-wire bus
etc is so easy on the 8031.

<vkesler@gmail.com> schrieb im Newsbeitrag 
news:1154532425.814367.195320@s13g2000cwa.googlegroups.com...
> <@> wrote:
>> Hello
>>
>> I am new to the 8051 compatible controller. I am used to PIC as well as
>> Renesas and using C.
>> The 8051 does not have a "Port Direction" to set. I have some questions
>> regarding this:
>>
>> - How to set it as input? I read something of writing 1 to the latch.
>> However, this is as using it as output and set it. I don't get its 
>> function.
>> - How to set it as output correctly?
>> - There is a difference between reading the "pin" and reading "latch". 
>> Can I
>> somehow select which one I want to read?
>
> The 8051 port pins have weak pull-ups, which means if you set them to
> '1', you can use them as inputs. There is nothing else you can or must
> do to use a pin as an input.
> You can't read back the latch AFAIK.
>
> If you want to use it as a an output, you don't need to do anything
> either, unless you need more drive on the high side, in which case you
> add a pull-up resistor or a buffer.
>
> This is why doing open collector type routines like I2C, one-wire bus
> etc is so easy on the 8031.
>

Thanks a lot.
Franz

There's a good web site.... www.8052.com , that has a good forum, and 
tutorial web page.

The wording for the "classic" 80c51 ports  is  called Quasi-Bidirectional.

Check out these

a.. '51 "Bible" Family Architecture (PDF): Chapter 1: '51 family of 
microcontrollers, architectural overview
a.. '51 "Bible" Hardware Description (PDF): Chapter 3: '51 Hardware 
description- stuff that is not in data sheets any more
a.. '51 "Bible" Programmers Guide (PDF): Chapter 2: '51 programmers guide 
and instruction set


http://www.8052.com/links.phtml


Regards
Joseph




<@> wrote in message news:44d0cb9d$1_1@news.tiscalinet.ch...
> <vkesler@gmail.com> schrieb im Newsbeitrag 
> news:1154532425.814367.195320@s13g2000cwa.googlegroups.com...
>> <@> wrote:
>>> Hello
>>>
>>> I am new to the 8051 compatible controller. I am used to PIC as well as
>>> Renesas and using C.
>>> The 8051 does not have a "Port Direction" to set. I have some questions
>>> regarding this:
>>>
>>> - How to set it as input? I read something of writing 1 to the latch.
>>> However, this is as using it as output and set it. I don't get its 
>>> function.
>>> - How to set it as output correctly?
>>> - There is a difference between reading the "pin" and reading "latch". 
>>> Can I
>>> somehow select which one I want to read?
>>
>> The 8051 port pins have weak pull-ups, which means if you set them to
>> '1', you can use them as inputs. There is nothing else you can or must
>> do to use a pin as an input.
>> You can't read back the latch AFAIK.
>>
>> If you want to use it as a an output, you don't need to do anything
>> either, unless you need more drive on the high side, in which case you
>> add a pull-up resistor or a buffer.
>>
>> This is why doing open collector type routines like I2C, one-wire bus
>> etc is so easy on the 8031.
>>
>
> Thanks a lot.
> Franz
>
> 

@ wrote:
> Hello
> 
> I am new to the 8051 compatible controller. I am used to PIC as well as 
> Renesas and using C.
> The 8051 does not have a "Port Direction" to set. I have some questions 
> regarding this:
> 
> - How to set it as input? I read something of writing 1 to the latch. 
> However, this is as using it as output and set it. I don't get its function.
> - How to set it as output correctly?
> - There is a difference between reading the "pin" and reading "latch". Can I 
> somehow select which one I want to read?

This also depends somewhat on the variant.
The orginal 80C51 used a quasi-bidirectional port : Strong N FET with
dymamic P fet and lighter holding P FET.
This makes Wire OR and two way links like i2c ans 2 wire, very easy.
The data sheets explain which opcodes read the pins, and which read the
latch; there is no port set-up as such.

Newer variants have 4 mode port pins : (and these do need a port set-up)
Std C51
CMOS Drive
Open Drain
Input

Examples are Silabs devices, Philips LPC9xx, Atmel AT89LPxx, Winbond 
W79E8xx series, (etc)

These allow almost any design to be implemented, on a per-pin granularity.

Open drain without pullups, is good for very low power keypad idle 
appliations,
Input only allows higher impedence drive sources
( mains zero crossing )
CMOS drive is good for LED or large FET drive.

-jg

Ah!

Heres a good start

http://www.8052.com/forum/read.phtml?id=121603



<@> wrote in message news:44d0bb33$1_1@news.tiscalinet.ch...
> Hello
>
> I am new to the 8051 compatible controller. I am used to PIC as well as 
> Renesas and using C.
> The 8051 does not have a "Port Direction" to set. I have some questions 
> regarding this:
>
> - How to set it as input? I read something of writing 1 to the latch. 
> However, this is as using it as output and set it. I don't get its 
> function.
> - How to set it as output correctly?
> - There is a difference between reading the "pin" and reading "latch". Can 
> I somehow select which one I want to read?
>
> Thanks for your help
> Franz
>
> 

Thanks to all of you guys.
You're a great help. The 8052.com indeed is a good place to start and Kai's 
description clarified all.

Thanks a lot!
Franz

"Joe G (Home)" <joe.g@optusnet.com.au> schrieb im Newsbeitrag 
news:44d20609$0$1211$afc38c87@news.optusnet.com.au...
> Ah!
>
> Heres a good start
>
> http://www.8052.com/forum/read.phtml?id=121603
>
>
>
> <@> wrote in message news:44d0bb33$1_1@news.tiscalinet.ch...
>> Hello
>>
>> I am new to the 8051 compatible controller. I am used to PIC as well as 
>> Renesas and using C.
>> The 8051 does not have a "Port Direction" to set. I have some questions 
>> regarding this:
>>
>> - How to set it as input? I read something of writing 1 to the latch. 
>> However, this is as using it as output and set it. I don't get its 
>> function.
>> - How to set it as output correctly?
>> - There is a difference between reading the "pin" and reading "latch". 
>> Can I somehow select which one I want to read?
>>
>> Thanks for your help
>> Franz
>>
>>
>
>