Maxim Integrated Secure Microcontroller - Manual (Page 169)

Secure Microcontroller User’s Guide
169 of 187
lcall OPEN ;Set up to read date/time.
mov B #8 ;Set up to send 8 bytes.
F:
lcall
RBYTE ;Read a byte of date/time.
G:
jnb
TI, G ;Wait for end of previous send.
clr TI ;Clear transmitter.
mov SBUF, A ;Send out the byte.
djnz B, F ;Loop for 8 bytes.
sjmp L ;Return to main loop.
H:
cjne
A, #’W’, J ;Skip if not a write.
lcall OPEN ;Set up to read date/time.
mov B, #8 ; Set up to receive 8 bytes.
I:
jnb
RI, I ;Wait to receive a byte.
jlr RI ;Clear the receiver.
mov A, SBUF ;Bring in the byte.
lcall WBYTE ;Write a byte of date/time.
djnz B, I ;Loop for 8 bytes.
sjmp L ;Return to main loop.
J:
jnb
TI, J ;If it is neither an R nor a W
clr TI ;increment the character,
inc A ;send it back out to the
mov SBUF, A ;serial port, and then
sjmp L ;return to the main loop.
;
;
; SUBROUTINE TO OPEN THE CLOCK/CALENDAR (ECC)
;
; This subroutine executes the sequence of reads and writes which
; is required in order to open communication with the timekeeper.
; The subroutine returns with the timekeeper opened for data
; access with both the accumulator and B register modified.
;
OPEN:
LCALL CLOSE ;Make sure it is closed.
MOV B,#4 ;Set pattern period count.
MOV A,#0C5H ;Load first byte of pattern.
OPENA: LCALL WBYTE ;Send out the byte.
XRL A,#0FFH ;Generate next pattern byte.
LCALL WBYTE ;Send out the byte.
SWAP A ;Generate next pattern byte.
DJNZ B,OPENA ;Repeat until 8 bytes sent.
RET ;Return.
;
;********************************
;*** SUBROUTINE TO CLOSE THE RTC
;********************************
;
; This subroutine insures that the registers of the timekeeper ; are closed
by executing 9 successive reads of the date and time ; registers. The
subroutine returns with both the accumulator ; and the B register modified.
;
CLOSE: MOV
B,#9 ;Set up to read 9 bytes.
CLOSEA: LCALL RBYTE ;Read a byte.
DJNZ B,CLOSEA ;Loop for 9 byte reads.
RET ;Return.
;
;***********************************
;*** SUBROUTINE TO READ A DATA BYTE