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enCoRe™ V CY7C643xx, enCoRe™ V LV CY7C604xx TRM, Document No. 001-32519 Rev *H
76
External Crystal Oscillator (ECO)
10.3
Register Definitions
These registers are associated with the external crystal oscillator.
10.3.1
ECO_ENBUS Register
The ECO_ENBUS register is used to disable and enable the
external crystal oscillator (ECO).
Bits 2 to 0 ECO_ENBUS[2:0].
111b – Default. Disables the
external crystal oscillator (ECO).
011b – Allows the ECO to be enabled by bits in the
ECO_CFG register.
Other values are reserved. See the
for the proper sequence for enabling the ECO.
For additional information, refer to the
10.3.2
ECO_TRIM Register
The ECO TRIM Register (ECO_TRIM) controls gain and
power settings for the 32-kHz crystal oscillator.
These settings should not be changed from their default
state. The default value is 14h.
Bits 4 to 2: ECO_XGM[2:0].
These bits set the amplifier
gain. In high-power mode (ECO_LPM=0), the step size of
the current source is approximately 400 nA, and the highest
source current is with the '000' setting. In low-power mode
(ECO_LPM=1), the overall power is approximately 5% lower
with the '000' setting than with the '111' setting.
’000’ is the highest gain setting, and has the lowest power in
low-power mode (5% power reduction).
’111’ is the lowest gain setting.
This value is factory trimmed; the typical value is '101'.
Bits 1 to 0: ECO_LP[1:0].
These bits set the gain mode.
’00’ is the highest power setting.
’11’ is the lowest power setting. (30% power reduction).
The default value is '00'.
For additional information, refer to the
10.3.3
ECO_CFG Register
The ECO Configuration Register provides status and control
for the ECO.
Bit 2 ECO_LPM.
This bit enables the ECO low-power
mode when high. This is recommended for use only during
sleep mode.
Bit 1 ECO_EXW.
The ECO Exists Written bit is used as a
status bit to indicate that the ECO EX bit was previously writ-
ten to. It is read only. When this bit is a '1' indicates that the
ECO_CFG register was written to and is now locked.
Bit 0 ECO_EX.
The ECO Exists bit serves as a flag to the
hardware, to indicate that an external crystal oscillator exists
in the system. Just after boot, it may be written only once to
a value of '1' (crystal exists) or '0' (crystal does not exist).
If the bit is '0', a switch-over to the ECO is locked out by
hardware. If the bit is '1', hardware allows the firmware to
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Access
1,D2h
ECO_ENBUS[2:0]
RW : 07
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Access
1,D3h
ECO_XGM[2:0]
ECO_LP[1:0]
RW : 11
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Access
1,E1h
ECO_LPM
ECO_EXW
ECO_EX
RW : 00