BCM20730 Data Sheet
Functional Description
Section 1: Functional Description
Keyboard Scanner
The keyboard scanner is designed to autonomously sample keys and store them into buffer registers without
the need for the host microcontroller to intervene. The scanner has the following features:
• Ability to turn off its clock if no keys pressed.
• Sequential scanning of up to 160 keys in an 8 x 20 matrix.
• Programmable number of columns from 1 to 20.
• Programmable number of rows from 1 to 8.
• 16-byte key-code buffer (can be augmented by firmware).
• 128 kHz clock – allows scanning of full 160-key matrix in about 1.2 ms.
• N-key rollover with selective 2-key lockout if ghost is detected.
• Keys are buffered until host microcontroller has a chance to read it, or until overflow occurs.
• Hardware debouncing and noise/glitch filtering.
• Low-power consumption. Single-digit µA-level sleep current.
Theory of Operation
The key scan block is controlled by a state machine with the following states:
Idle
The state machine begins in the idle state. In this state, all column outputs are driven high. If any key is pressed,
a transition occurs on one of the row inputs. This transition causes the 128 kHz clock to be enabled (if it is not
already enabled by another peripheral) and the state machine to enter the scan state. Also in this state, an 8-
bit row-hit register and an 8-bit key-index counter is reset to 0.
Scan
In the scan state, a row counter counts from 0 up to a programmable number of rows minus 1. Once the last
row is reached, the row counter is reset and the column counter is incremented. This cycle repeats until the
row and column counters are both at their respective terminal count values. At that point, the state machine
moves into the Scan-End state.
As the keys are being scanned, the key-index counter is incremented. This counter is the value compared to the
modifier key codes stored, or in the key-code buffer if the key is not a modifier key. It can be used by the
microprocessor as an index into a lookup table of usage codes.
BROADCOM
®
September 9, 2013 • 20730-DS108-R
Page 12
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