Timer Operation - Renesas H8 Series Hardware Manual

Timer Load Register B1 (TLB1)
Bit
TLB17
Initial value
Read/Write W
TLB1 is an 8-bit write-only register for setting the reload value of timer counter B1 (TCB1).
When a reload value is set in TLB1, the same value is loaded into timer counter B1 (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.
The same address is allocated to TLB1 as to TCB1.
Upon reset, TLB1 is initialized to H'00.
9.3.3

Timer Operation

Interval Timer Operation: When bit TMB17 in timer mode register B1 (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 clock input to timer B1 is selected from seven internal clock
signals output by prescaler S, or an external clock input at pin TMIB. The selection is made by bits
TMB12 to TMB10 of TMB1.
After the count value in TCB1 reaches H'FF, the next clock signal input causes timer B1 to
overflow, setting bit IRRTB1 to 1 in interrupt request register 1 (IRR1). If IENTB1 = 1 in
interrupt enable register 1 (IENR1), a CPU interrupt is requested.*
At overflow, TCB1 returns to H'00 and starts counting up again.
During interval timer operation (TMB17 = 0), when a value is set in timer load register B1
(TLB1), the same value is set in TCB1.
Note: * For details on interrupts, see section 3.3, Interrupts.
7 6 5
TLB16 TLB15
0 0 0
W W
4 3
TLB14 TLB13 TLB12
0 0
W W
Rev. 6.00 Sep 12, 2006 page 213 of 526
Section 9 Timers
2 1 0
TLB11 TLB10
0 0 0
W W W
REJ09B0326-0600