
VRS550 / VRS560
VERSA
Datasheet Rev 1.1
1134 Ste Catherine Street West, Suite 900, Montreal, Quebec, Canada H3B 1H4
Tel: (514) 871-2447
http://www.goalsemi.com
28
The table below gives examples of Watchdog timeout
period the user will obtain for different values of the
WDPSx bits of the Watch Dog Timer Register.
T
ABLE
23:
W
ATCH
D
OG
T
IMER PERIOD VS
. WDWDPS [2:0]
BIT
Fosc Division
WDPS [2:0]
Factor
WDT
Timeout
(ms) @
20MHz
26.2
000
8
001
16
52.4
010
32
104.8
011
64
209.7
100
128
419.4
101
110
111
256
512
1024
838.8
1677.7
3355.4
The System Control Register
The System Control register is used to monitor the
status of the Watch Dog Timer and inhibit the address
Latch Enable signal output.
T
ABLE
24:
T
HE
S
YSTEM
C
ONTROL
R
EGISTER
(SYSCON)–SFR BF
H
7
6
5
WDRESET
Unused
Bit
Mnemonic
Description
7
WDRESET
Watch Dog Timer Reset Status Bit
[6:3]
Unused
-
2
Unused
-
1
Unused
-
0
ALEI
1: Enable Electromagnetic Interference
Reducer
0: Disable Electromagnetic Interference
Reducer
4
3
2
1
0
XRAME
ALEI
The WDRESET bit of the SYSCON register is the
Watch Dog Timer Reset bit. It will be set to 1 when a
reset signal is generated by the WDT overflow. The
user should check the WDRESET bit state if a reset
has taken place in application where the Watch Dog
timer is activated
Reduced EMI Function
The VRS550 and the VRS560 devices can also be set
up to reduce its EMI (electromagnetic interference) by
setting bit 0 (ALEI) of the SYSCON register to 1. This
function will inhibit the Fosc/6Hz clock signal output to
the ALE pin.
Crystal Consideration
The crystal connected to the VRS550 / VRS560
oscillator input should be of a parallel type, operating in
fundamental mode.
The following table shows the value of capacitors and
feedback resistor that must be used at different
operating frequencies.
XTAL
3MHz
6MHz
C1
30 pF
30 pF
C2
30 pF
30 pF
R
open
open
Note:
Oscillator circuits may differ with different
crystals or ceramic resonators in higher oscillation
frequency.
12MHz
30 pF
30 pF
open
16MHz
30 pF
30 pF
open
25MHz
15 pF
15 pF
62K
Crystals or ceramic resonator characteristics vary from
one manufacturer to the other.
The user should check the specific crystal or ceramic
resonator technical literature available or contact the
manufacturer to select the appropriate values for the
external components.
VRS550
VRS560
XTAL1
XTAL2
XTAL
R
C1
C2