Maxim Integrated MAXQ610 - Manual (Page 81)

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MAXQ610 User’s Guide
REGISTER DESCRIPTION
WUTC (04h, 01h) Wake-Up Timer Control Register (8-bit register)
Initialization: This register is cleared to 00h on all resets .
Read/Write Access: Unrestricted read/write access except that bit 1 is read-only .
WUTC.0 (WTE) Wake-Up Timer Enable. This control bit enables down counting of the 16-bit wake-up
timer . Clearing this bit resets the internal wake-up timer down counter and resets WTF =
0 . When WTE = 0, the initial down-counter starting value written into the WUT register is
accessed on WUT register reads . Setting this bit from 0 to 1 loads the internal down counter
with the initial value written to the WUT register, and enables down counting of the wake-up
timer using the ring oscillator . When WTE = 1, the internal down counter value is accessed
on WUT register reads . When WTE = 1, hardware setting of the WTF bit can generate an
interrupt request to the CPU if also enabled globally .
WUTC.1 (WTF) Wake-Up Timer Flag. This bit serves as a status bit/interrupt flag to denote when the wake-
up timer down count has reached 0h . Hardware sets this bit whenever the wake-up down
counter reaches 0h . The WTF bit is cleared by hardware any time the WTE bit is changed
from 1 to 0 .
WUTC.7 to WUT.2 Reserved . Reads return 0 .
WUT (05h, 01h) Wake-Up Timer Register (16-bit register)
Initialization: This register is cleared to 0000h on all resets .
Read/Write Access: Unrestricted write access .
When WTE = 0, reads access the initial starting value written to WUT . When WTE = 1, reads
access the internal down counter, thus multiple reads should be made to attain a stable
value
WUT.15 to WUT.0 Wake-Up Timer Value Register Bits 15:0. These bits reflect the 16 bit value of the Wake-
Up Timer . When WTE = 0, the initial wake-up timer starting value may be accessed by
reads and writes of the WUT register . This initial starting value is retained internally so that
triggering another wake-up timer interval requires only toggling of the WTE bit 1 ≥ 0 ≥ 1 .
When WTE = 1, the internal down-counter value is accessed by reads of WUT, however,
write access is still directed to the initial starting value (that is loaded to the down counter
each time WTE is changed 0 ≥ 1) . The 16-bit wake-up timer counts downward until reach-
ing 0h unless disabled . The internal down counter is asynchronously reset to 0 anytime the
wake-up timer is disabled by clearing WTE = 0 . Once started, the WTF flag is set by hard-
ware when the down count reaches 0h . The 0FFFFh starting state for the WUT[15:0] bits
yield the maximum possible down-count range . Writing the WUT[15:0] bits establishes the
down-count starting values shown below:
WUT[15:0] DOWN-COUNT START VALUE
0001h 1
0002h 2
0003h 3
0004h 4
--Other-- (WUT[15:0])
0FFFEh (2 16 - 2) = 65,534
0FFFFh (2 16 - 1) = 65,535
PI4 (08h, 01h) Port 4 Input Register
Initialization: The reset value for this register is dependent on the logical states of the pins .
Read/Write Access: Unrestricted read .
PI4.5 to PI4.0 Port 4 Input Register Bits 5:0. The PI4 register always reflects the logic state of its pins
when read . Note that each port pin has a weak pullup circuit when functioning as an input
and the p-channel pullup transistor is controlled by its respective PO bits . If the PO bit is set
to 1, the weak pullup is on, if the PO bit is cleared to 0, the weak pullup is off and forces the
port pin into three-state .
PI4.7 to PI4.6 Reserved . Reads return 0 .