DS80CH11 Maxim, DS80CH11 Datasheet - Page 59

• Manufacturer Part Number: DS80CH11
• Description: The system energy manager is a highly integrated microcontroller that provides several key features for systems including key scanning and control, battery and power management, as well as two 2-Wire serial I/O Ports
• Manufacturer: Maxim

10.0 KEYBOARD SCANNING PORTS
10.1 OVERVIEW
Three 8–bit I/O ports are provided which can be used for
key matrix scan line outputs and inputs. Ports 8 and 9
are intended for scan line outputs, while port 4 is
intended for scan line inputs.
10.2 KEY SCAN OUTPUTS
Ports 8 and 9 together provide 16 open–drain lines
which are intended for use as key scan outputs. These
lines are logically accessed and operated as normal
pseudo–bi–directional I/O port pins. As a result, lines
which are not required for the key scan function can be
used as general purpose I/O for the control of other
functions.
10.3 KEY SCAN INPUTS
Port 4 is a parallel I/O port which is logically and electri-
cally tailored for keyboard matrix scan inputs. All of the
port 4 pins are Schmitt triggered inputs and are inter-
nally pulled high by a resistor. In addition, all pins are
10.4 KDE – KEY DETECT ENABLE REGISTER
KDE; SFR ADDR.=0A5H
Read/Write Access: Unrestricted.
Initialization: Undefined on any type of reset
KDE7–KDE0 – Key Detect Enable Bits
When a KDEn enable bit is set, it enables negative–
edge transition detection on the corresponding line of
10.5 KDF – KEYBOARD DETECT FLAG REGISTER
KDF; SFR ADDR.=0A6H
Read/Write Access: Unrestricted read; all bits write only to 0.
Initialization: 00H on any type of reset
KDFn are flag bits for the keyboard activity detection. If
a port 4–pin has its KDEn bit set, the corresponding
KDFn is set when an negative edge is detected on that
pin. An SEM interrupt will be recognized if the KDEn bit
is set and the interrupts are enabled. Upon receipt of the
interrupt, the system should read this register to deter-
mine on which scan line the key closure occurred. The
KDE7
BIT 7
BIT 7
KDF7
KDE6
KDF6
BIT 6
BIT 6
KDE5
KDF5
BIT 5
BIT 5
KDE4
KDF4
BIT 4
BIT 4
capable of generating an interrupt on a low–going tran-
sition. As a result, the SEM can initiate a keyboard scan
only when a key is pressed instead of doing it periodi-
cally. Thus, battery drain is minimized.
In order to use a Port 4 pin as a key scan input, its output
latch bit in the Port 4 SFR register must be first written to
a 1, which configures the pin as an input. Negative tran-
sition detection on each pin is enabled by setting the
matching KDEn enable bit in the Keyboard Detect
Enable Register to a 1. Then, when a negative transi-
tion occurs on an enabled input, the corresponding
interrupt flag bit will be set in the Keyboard Detect Flag
Register. If the Key Detect Interrupt Enable bit is set
(EKD; register EIE.5), a keyboard interrupt will then be
recognized by the SEM core. Upon interrupt, the sys-
tem should scan the keyboard matrix via other output
ports (typically ports 8 and 9) to identify the location of
the pressed key. The set keyboard interrupt flag bits
should be cleared by firmware to clear the interrupt
condition before exiting the interrupt service routine.
port 4. When a KDEn bit is cleared no transition detec-
tion is performed on the corresponding line.
firmware can then scan the keyboard matrix using Ports
8 and 9 as outputs to identify the location of the
depressed key. In order to clear the interrupt condition,
the firmware should clear the interrupting KDF bit(s) by
writing 00H to the KDF register prior to exiting the inter-
rupt service routine.
KDE3
BIT 3
BIT 3
KDF3
KDE2
KDF2
BIT 2
BIT 2
KDE1
KDF1
BIT 1
BIT 1
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KDE0
KDF0
BIT 0
BIT 0
DS80CH11