BS1-based

Archiver

Hi all!!! With the project I'm currently working on, it is necessary for
several Stamp 2's to communicate with one-another. So, after much
brainstorming, I have decided to use a single BS1 as "voice mail" for the
other Stamps. Each BS2 will be able to send data to the BS1 with a data
prefix, telling the BS1 which BS2 the data is intended for. Then, when each
BS2 gets to a certain point in its program, it will request data from the
BS1, and retrieve it if the data is there... I plan on doing this with I/O
lines 0-3 on the BS1 connect to Tx, Rx, I/O 0, & I/O 1 on each BS2, forming a
four line bus.

The communication protocol would be as fallows:
A BS2 checks line 4 (between BS1 I/O #3, & BS2 I/O #1) is low, if so, the BS2
makes line 4 high, and then waits a set time for the BS1 to prepare to
receive. After this time, the BS2 sends out identifying data on line 3
(between BS1 I/O #2, & BS2 I/O #0) , the first part, (probably 3 bits)
identifies the BS2 that is communicating with the BS1 (one of a possible
eight BS2's), then, the second part (1 or 2 bits) of the data tells the BS1
whether the BS2 is sending or retrieving data. If retrieving, the BS2 will
immediately prepare to receive the data, and at the same time the BS1 will
retrieve the data by finding a data string with the data prefix identifying
the intended BS2 receiver, wait an amount of time if necessary, then send the
data, if there is no data the BS1 will simply send a string of 0's. If the
BS2 is sending data, then the BS1 will prepare to receive, while the BS2 will
prepare the data, with a prefix identifying the BS2 that the data is intended
for, then send the data. When the BS2 is finished with the BS1, it will take
line 4 low again, so that other BS2's can communicate with the BS1. Data
going from BS1 to BS2 will be on line 2. Data going from BS2 to BS1 will be
on line 1.

Does anyone see any problems with this? The protocol seems sound to me,
the only problem I see, would be if two BS2's took line 4 high at _exactly_
the same time, and then tried to communicate with the BS1 simultaneously. But
how likely is that?!? And one more problem... Data storage. I have four lines
left on the BS1, and will need to hook up a memory device (at least 512 bytes
storage). Except that it is not this easy. I need to store the data in some
way, so that I can retrieve the data for each BS2. Any ideas???

So, if anyone can think of any potential problems, or improvements on this
idea, let me know.


Thanks in advance,
Edward Kindler

Archiver

Edward:

It would seem to me that the use of Line 3 (sending ID info from BS2
to BS1) could happen on the Line 1, thus saving you a line.

One method that occurs to me to prevent the simultaneous broadcasts
(I'm not really a hardware type, so this is somewhat speculative) is
to have each of the 8 BS2's apply a different specific voltage to the
Line 4. Have an a/d on the BS1. If the a/d resolution is sufficient,
you should be able to assign the BS2's voltages so that you could tell
if only one was broadcasting, or if multiple ones were. The Line 3
could be raised momentarily by the BS1 to tell all BS2's to shutup and
start over when Line 3 is lowered (use a random time after which to
restart; or specifically code a different time for each BS2).

A variation on the above would be to have the BS1 momentarily raise
Line 3 to restart the communications if it was unable to decipher the
data received on Line 1. Maybe you would consider some sort of
checksum or parity byte as part of the transmitted packet.

Another alternative; a polling approach. If timing is not critical,
have the BS1 poll the BS2's. BS1 sends poll message (3-bits that
identify which BS2) on Line 3 and wait for a response on Line4--if no
response within a timeout time, go on to the next BS2 poll. If the
polled BS2 wants to chat, it responds by raising Line 4. If the BS1
sees Line 4 go high, it then waits for the BS2 to transmit the info on
Line 1--if there in no data to send from the BS2, it sends a special
code to say so. Then the BS1 sends any messages stored for that BS2
on Line 2--maybe a code that is either "no message" or a count of
messages, followed by the messages. When the BS2 is finished
receiving the messages, it drops Line 4. Then the BS1 continues its
round-robin polling with the next BS2.

Just thinking out loud.

BTW, you might be interested in taking a look at
http://www.ibutton.com/csp.html and
http://www.ibutton.com/software/1wire/wirekit.html .

Regards,
Daniel

---

Original Message

---

From: <RiffRaff82@a...>
To: <basicstamps@egroups.com>
Sent: Wednesday, June 21, 2000 03:52 PM
Subject: [noparse][[/noparse]basicstamps] BS1-based "voice mail"


> Hi all!!! With the project I'm currently working on, it is
necessary for
> several Stamp 2's to communicate with one-another. So, after much
> brainstorming, I have decided to use a single BS1 as "voice mail"
for the
> other Stamps. Each BS2 will be able to send data to the BS1 with a
data
> prefix, telling the BS1 which BS2 the data is intended for. Then,
when each
> BS2 gets to a certain point in its program, it will request data
from the
> BS1, and retrieve it if the data is there... I plan on doing this
with I/O
> lines 0-3 on the BS1 connect to Tx, Rx, I/O 0, & I/O 1 on each BS2,
forming a
> four line bus.
>
> The communication protocol would be as fallows:
> A BS2 checks line 4 (between BS1 I/O #3, & BS2 I/O #1) is low, if
so, the BS2
> makes line 4 high, and then waits a set time for the BS1 to prepare
to
> receive. After this time, the BS2 sends out identifying data on line
3
> (between BS1 I/O #2, & BS2 I/O #0) , the first part, (probably 3
bits)
> identifies the BS2 that is communicating with the BS1 (one of a
possible
> eight BS2's), then, the second part (1 or 2 bits) of the data tells
the BS1
> whether the BS2 is sending or retrieving data. If retrieving, the
BS2 will
> immediately prepare to receive the data, and at the same time the
BS1 will
> retrieve the data by finding a data string with the data prefix
identifying
> the intended BS2 receiver, wait an amount of time if necessary, then
send the
> data, if there is no data the BS1 will simply send a string of 0's.
If the
> BS2 is sending data, then the BS1 will prepare to receive, while the
BS2 will
> prepare the data, with a prefix identifying the BS2 that the data is
intended
> for, then send the data. When the BS2 is finished with the BS1, it
will take
> line 4 low again, so that other BS2's can communicate with the BS1.
Data
> going from BS1 to BS2 will be on line 2. Data going from BS2 to BS1
will be
> on line 1.
>
> Does anyone see any problems with this? The protocol seems sound
to me,
> the only problem I see, would be if two BS2's took line 4 high at
_exactly_
> the same time, and then tried to communicate with the BS1
simultaneously. But
> how likely is that?!? And one more problem... Data storage. I have
four lines
> left on the BS1, and will need to hook up a memory device (at least
512 bytes
> storage). Except that it is not this easy. I need to store the data
in some
> way, so that I can retrieve the data for each BS2. Any ideas???
>
> So, if anyone can think of any potential problems, or
improvements on this
> idea, let me know.
>
>
> Thanks in advance,
> Edward Kindler
>
>
>
>
>