One way to handle your requirement would be as below :

1. Wait for 100ms
2. Read Port 0
3. Move it to ACC
4. Call SNDBYT
5. Handle the two ASCII values in VB
6. Jump to step 1

I have given below two assembly routines - SNDTXT will send one ASCII value (in ACC) and the SNDBYT will send two ASCII values corresponding to the value of the accumulator. Use as required.

For the whole thing to work your VB code must be done properly - much easier to use the ComEvent. Idea is to have it ready to recieve when the MCU is ready to send.

;==============================================

SNDTXT:   NOP                ;send text pointed at by DPTR
          MOV A, #0
          MOVC A, @A+DPTR
          CALL SND232        ; move it to com port
          RET

SND232:   JNB  SCON.1, $     ; wait for previous character to go..
          CLR  SCON.1        ; and send current character to COMM
          MOV  SBUF,  A
          RET

;================================================

SNDBYT:   PUSH ACC           ; send hex BYTE - each nibble as ASCII
          SWAP A             ; Will send Hi nibble first
          CALL SNDLOW        ; Sent.
          POP  ACC           ; Will send low nibble next
SNDLOW:   ANL  A, #0FH
          CLR  C
          ADD  A, #246
          JC   HEXOUT
          ADD  A, #58        ; 0 to 9 character
          JMP  SND232

SNDHEX:   ADD  A, #65        ; A to F character
          JMP  SND232

;==============================================

PS: The code must assemble without errors. Pulled out of a large code and labels corrected suitably.

Raghu