Maxim Integrated Secure Microcontroller User 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