HD64F3687HV Datasheet, PDF (190/538 Pages) Renesas Technology Corp – Renesas 16-Bit Single-Chip Microcomputer H8 Family/H8/300H Tiny Series

Section 11 Timer B1
11.3.3 Timer Load Register B1 (TLB1)
TLB1 is an 8-bit write-only register for setting the reload value of TCB1. When a reload value is
set in TLB1, the same value is loaded into TCB1 as well, and TCB1 starts counting up from that
value. When TCB1 overflows during operation in auto-reload mode, the TLB1 value is loaded
into TCB1. Accordingly, overflow periods can be set within the range of 1 to 256 input clocks.
TLB1 is allocated to the same address as TCB1. TLB1 is initialized to H'00.
11.4 Operation
11.4.1 Interval Timer Operation
When bit TMB17 in TMB1 is cleared to 0, timer B1 functions as an 8-bit interval timer. Upon
reset, TCB1 is cleared to H'00 and bit TMB17 is cleared to 0, so up-counting and interval timing
resume immediately. The operating clock of timer B1 is selected from seven internal clock signals
output by prescaler S, or an external clock input at pin TMB1. The selection is made by bits
TMB12 to TMB10 in TMB1.
After the count value in TMB1 reaches H'FF, the next clock signal input causes timer B1 to
overflow, setting flag IRRTB1 in IRR2 to 1. If IENTB1 in IENR2 is 1, an interrupt is requested to
the CPU.
At overflow, TCB1 returns to H'00 and starts counting up again. During interval timer operation
(TMB17 = 0), when a value is set in TLB1, the same value is set in TCB1.
11.4.2 Auto-Reload Timer Operation
Setting bit TMB17 in TMB1 to 1 causes timer B1 to function as an 8-bit auto-reload timer. When
a reload value is set in TLB1, the same value is loaded into TCB1, becoming the value from which
TCB1 starts its count. After the count value in TCB1 reaches H'FF, the next clock signal input
causes timer B1 to overflow. The TLB1 value is then loaded into TCB1, and the count continues
from that value. The overflow period can be set within a range from 1 to 256 input clocks,
depending on the TLB1 value.
The clock sources and interrupts in auto-reload mode are the same as in interval mode. In auto-
reload mode (TMB17 = 1), when a new value is set in TLB1, the TLB1 value is also loaded into
TCB1.
Rev.5.00 Nov. 02, 2005 Page 156 of 500
REJ09B0027-0500