Datasheet

MRF49XA
DS70590C-page 40 Preliminary © 2009-2011 Microchip Technology Inc.
EQUATION 2-9:
REGISTER 2-16: BCSREG: BATTERY THRESHOLD DETECT AND CLOCK OUTPUT VALUE SET
REGISTER (POR: 0xC000)
W-1 W-1 W-0 W-0 W-0 W-0 W-0 W-0
CCB<15:8>
bit 15 bit 8
W-0 W-0 W-0 W-0 W-0 W-0 W-0 W-0
COFSB<2:0>
r LBDVB<3:0>
bit 7 bit 0
Legend: r = reserved bit
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown
bit 15-8 CCB<15:8>: Command Code bits
The command code bits (11000000b) are serially sent to the microcontroller to identify the bits to be
written in the BCSREG.
bit 7-5 COFSB<2:0>: Clock Output Frequency Set bits
These bits set the output clock frequency which can be used to run an external host microcontroller.
111 = 10 MHz
110 = 5 MHz
101 = 3.33 MHz
100 = 2.5 MHz
011 = 2 MHz
010 = 1.66 MHz
001 = 1.25 MHz
000 = 1 MHz
bit 4 Reserved: Write as ‘0’
bit 3-0 LBDVB<3:0>: Low Battery Detect Value bits
These bits set the decimal value to calculate the battery detect threshold voltage level
(1,2)
.
Note 1: When the battery level goes down by 50 mV below this value, the LBTD bit (STSREG<10>) is set, indicating
that the battery level is below the programmed threshold. This is useful in monitoring discharge-sensitive
batteries, such as Lithium cells. The low battery detect can be enabled by setting the LBDEN bit
(PMCREG<2>) and can be disabled by clearing the bit.
2: The low battery threshold value is programmable from 2.2V – 3.8V by using Equation 2-9.
Threshold Voltage Value = 2.25 +[0.1 x (LBDVB<3:0>)]
where:
LBDVB<3:0> is the Decimal Value from 0 to 15.