H838024 datasheet(351/697 Pages) RENESAS

351 / 697 page

Section 9 Timers

Rev. 7.00 Mar 10, 2005 page 309 of 652

REJ09B0042-0700

9.6.3

Timer Operation

The watchdog timer has an 8-bit counter (TCW) that is incremented by clock input. The input

clock is selected by the WDCKS in port mode register 2 (PMR2): on the H8/38024, H8/38024S,

and H8/38024R Group,

φ/8192 is selected when WDCKS is cleared to 0, and φw/32 when set to 1.

On the H8/38124 Group, if WDCKS is cleared to 0 the clock selection is specified by the setting

of timer mode register W (TMW), and if WDCKS is set to 1 the

φw/32 clock source is selected.

When TCSRWE = 1 in TCSRW, if 0 is written in B2WI and 1 is simultaneously written in

WDON, TCW starts counting up. (Write access to TCSRW is required twice to turn on the

watchdog timer. However, on the H8/38124 Group WDON is set to 1 after a reset is cancelled,

TCW starts to be incremented even without gaining write access to TCSRW.) When the TCW

count value reaches H'FF, the next clock input causes the watchdog timer to overflow, and an

internal reset signal is generated one base clock (

φ or φ

SUB) cycle later. The internal reset signal is

output for 512 clock cycles of the

OSC clock. It is possible to write to TCW, causing TCW to

count up from the written value. The overflow period can be set in the range from 1 to 256 input

clocks, depending on the value written in TCW.

Figure 9.18 shows an example of watchdog timer operations.

H'F8

TCW overflow

Start

H'F8 is written

in TCW

H'F8 is written in TCW

Reset

Internal reset

signal

512

φOSC clock cycles

H'FF

H'00

TCW count

value

Example:

φ = 2 MHz and the desired overflow period is 30 ms.

The value set in TCW should therefore be 256

− 8 = 248 (H'F8).

2 • 106

• 30 • 10−3 = 7.3

8192

Figure 9.18 Typical Watchdog Timer Operations (Example)

H838024 Datasheet(PDF) 351 Page - Renesas Technology Corp

H838024 Datasheet(HTML) 351 Page - Renesas Technology Corp

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL