HT37B90/HT37B70/HT37B50/HT37B30
Programming Considerations
directly written to the high byte register. At the same
time the data in the low byte buffer will be transferred
into its associated low byte register. For this reason,
when preloading data into the 16-bit timer registers, the
low byte should be written first. It must also be noted that
to read the contents of the low byte register, a read to
the high byte register must first be executed to latch the
contents of the low byte buffer into its associated low
byte register. After this has been done, the low byte reg-
ister can be read in the normal way. Note that reading
the low byte timer register will only result in reading the
previously latched contents of the low byte buffer and
not the actual contents of the low byte timer register.
As the 16-bit Timers have both low byte and high byte
timer registers, accessing these registers is carried out
in a specific way. It must be noted that when using in-
structions to preload data into the low byte registers,
namely TMRAL or TMRAL, the data will only be placed
into a low byte buffer and not directly into the low byte
register. The actual transfer of the data into the low byte
register is only carried out when a write to its associated
high byte register, namely TMRAH or TMRBH, is exe-
cuted. However, using instructions to preload data into
the high byte timer register will result in the data being
Program Example
External RC oscillation converter mode example program - Timer A overflow:
clr RCOCCR
mov a, 00000010b
mov RCOCR,a
clr intch.5
; Enable External RC oscillation mode and set Timer A overflow
; Clear External RC Oscillation Converter interrupt request flag
mov a, low (65536-1000); Give timer A initial value
mov tmral, a
mov a, high (65536-1000)
mov tmrah, a
mov a, 00h
; Timer A count 1000 time and then overflow
; Give timer B initial value
mov tmrbl, a
mov a, 00h
mov tmrbh, a
mov a, 00110000b
mov RCOCCR, a
p10:
; Timer A clock source=fSYS/4 and timer on
clr wdt
Snz intch.5
jmp p10
clr intch.5
; Program continue
; Polling External RC Oscillation Converter interrupt request flag
; Clear External RC Oscillation Converter interrupt request flag
Rev. 1.00
51
June 22, 2017
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
