THE
SIMPLIFIED THEORY |
We will see in this chapter, the commands to send and reveive
bytes on the serial and infrared port of the hp48. As I told into the Basic system, we got
3 forms of programmation languages. The basic RPL , the sytem RPL and the
assembly language (lthe other langages are the derivative of the two last).In RPL,
the commands to exchange bytes on the serial port and Infrared port are common.
One of the two port has to be selected before the use of such
commands:
->Select under HP48G/GX, in the
"transfer" list under menu I/O:
 |
-Here we set wire to choose the serial port (for IR
, choose Infrared)
-The protocol can be either Kermit or X/Ymodem
-The format ASC (ASCII text) or BIN (binary)
-The trnsfert rate is here de 9600 bauds
-No parity bit |
->Under the HP48 S/SX, inside the submenu setup
of the menu I/O
We got the same type of information: IR/WIRE, ASCII/BINARY;baud,
parity, checksum type et translate code. (The last two are never changed or used) |
A - The inputs/Outputs commands in RPL
1) Emission of a byte or a stringon a port
The command to use is XMIT. The synthax is defined as
below:
|
| Action |
Command |
| Send hello through a port |
"hello" XMIT |
| Send the A character (or byte) |
"A" XMIT |
| Send the character number X with X=0 to 255 |
X CHR XMIT |
The last action is very usefull. Two comments
should be done on one hand, XMIT open the serial port for you
(the infrared port nver need to be open) and do not forget to
close it behind with CLOSEIO, on the
other hand the return value is 1 if all is okay else 0. |
2) Reception of a charater on a port
a) Active lookup
|
| Action |
Command |
AExtract of X caracthers previously received
(X=1 to 255 character max) |
X SRECV |
The SRECV command opens the serial port and fetches charaters
into the input buffer. If none is present, the HP wait a while (TIMEOUT) and
gives either the received characters and the number received or an empty string with 0 (no
character received). Moreover, the hp48 is busy during this time and nothing else
can be accomplished.
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b) Passive lookup
Open the serial port with OPENIO and use SRECV to extract
on the fly the last received characters (before the input buffer overflow!).
If we force the emission of characters on the other side .(ie the
time between two RS232 is reduced), the HP becomes very slow (can not follow the rythm),
the busy indicator light on and the HP is in the state of key overflow . There is an
special limit of this (serial spawning) we can find, the duration between two serial
frames before the busy flag light on because it is the duration that gives best
serial response times.
When you have finished to transfer datas byte per byte, the best
is to closethe manualy port with CLOSEIO, as you will save your batteries.
This action is impossible to do when we overflow the input buffer (buffer) of the
hp.
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