Serial Buffer IC

 (Part Number: RSB509B)
(click here for PDF data sheet)

Overview

Protean Logic Inc.'s RSB509B is an easy to use, low cost IC that buffers RS232 serial data for a host microprocessor. The RSB509B stores up to 32 bytes of serial data received on the input pin and retransmits data to the host through the interface pin. The RSB509B frees the host microprocessor from serial data timing concerns. The real time considerations of RS232 interrupt handling are thus eliminated or reduced. Processors that emulate RS232 hardware via software, like the FBasic TICkit or the PARALLAX Basic STAMP, can perform other tasks while the RSB509B buffers serial data. The processor can retrieve the stored data when it has the time to spare by pulsing the interface pin. When using a TICkit or a STAMP as the host processor, the user program simply outputs a high on the interface pin immediately before the rs_receive or serin line.

Connecting the RSB509B is easy. Only a few pull down resistors and a crystal or resonator is required. The RSB509B only requires one connection line to the host processor.

Features

·             Small 8-pin plastic DIP package.

·             Requires 4MHz clock source (crystal or resonator); pull down resistors for data, empty, and ready outputs.

·             32 byte buffer transparently receives data and retransmits it to the host when requested.

·             Only one host processor pin required to completely interface to RSB509B.

·             Pulse protocol on the interface pin is used to program the RSB509B operation modes and to regulate data transfer.

·             Programmable input baud rates of 9600, 4800, 2400 or 1200. Lower baud rates possible by lowering clock frequency.

·             Receive input pin programmable for inverted (pull down) or non-inverted (RS232 driver output) signal polarity.

·             Interfaces with host at 9600 baud via open drain pin.

·             Host indicates it is ready to receive by bringing the data line high momentarily. Host emulation routine makes interface pin an input when it starts which inherently signals the RSB509B to send data from the buffer.

·             Programmable single byte or burst mode transferred to host.

·             Programmable byte match before buffer option for addressable packet reception.

·             Programmable break required before byte match option.

·             Buffer empty output and buffer full (/ready) output for handshaking and buffer status.

RSB509B Pin Assignments

 

 

Example Connection Diagrams

             

                 TICkit 62 Connection Diagram                                           STAMP™ II Connection Diagram

Example Software Control of RSB509B

TICkit 62 Sample Program

 

; Program for RSB509A serial buffering

 

DEF tic62_c

LIB fbasic.lib

LIB rsb509b.lib

 

FUNC none main

BEGIN

    ; generate a long pulse on interface pin to

    ; signal initialization to RSB509

    pin_high( pin_d0 )

    delay( 10 )

    =( in_err, pin_in( pin_d0 ))

 

    ; no match byte used but one must be sent

    ; as a place holder during initialization

    rs_param_set( rs_invert | rs_9600 | pin_d0 )

    rs_send( ' ' )

 

    ; serial input is inverted and 9600 baud.

    rs_send( rsb509_invert | rsb509_baud1 )

 

    ; wait for RSB509 to reset.

    delay( 100 )

    REPEAT

        ; generate a quick pulse for each

        ; byte to be read. pin high creates start

        ; of pulse. rs_receive creates end of pulse

        ; when it makes the pin an input.

        pin_high( pin_d1 )

 

        ; pin D1 will be used for input

        rs_param_set( rs_invert | rs_9600 | pin_d0 )

 

        ; read each byte with a short wait

        =( in_val, rs_receive( 100, 0b, in_err ))

        IF in_err

        ELSE

            rs_param_set( debug_pin )

            con_out_char( in_val )

        ENDIF

    LOOP

ENDFUN

 

 

Basic Stamp II Sample Program

 

' sample program for RSB509 on STAMP II

 

inval    VAR    byte

 

' generate a 10 ms pulse to signal initialization

HIGH 1

PAUSE 10

INPUT 1

 

' pin P1 is used for input.

' we are using open, inverted, 9600, 8N1 format

' no match byte is used but we must send a byte to

' hold our place during initialization

SEROUT 1, 49236, [" "]

 

' pin P1 is used for input.

' we are using on, inverted, 9600, 8N1 format

' serial input is inverted and 9600 baud

SEROUT 1, 49236, [%00000100]

 

' wait for RSB509 to reset

PAUSE 100

 

around:

' generate a quick pulse for each byte

' to be read. HIGH creates the start of

' the pulse. SERIN creates the end of the

' pulse when it makes the pin an input

' because the interface pin is pulled low

HIGH 1

 

' pin P1 is used for input.

' we are using open, inverted, 9600, 8N1 format

' if a byte is not received within 1 ms branch to

' "around" to poll again.

' data will only be displayed when byte is received

SERIN 1, 16468, 1, around, [inval]

 

' show character received on debug window

DEBUG inval

 

GOTO around

END