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ADP5585ACPZ-00-R7 Datasheet(PDF) 9 Page - Analog Devices |
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ADP5585ACPZ-00-R7 Datasheet(HTML) 9 Page - Analog Devices |
9 / 40 page Data Sheet ADP5585 Rev. C | Page 9 of 40 FUNCTIONAL DESCRIPTION EVENT FIFO Before going into detail on the various ADP5585 blocks, it is important to understand the function of the event FIFO. The ADP5585 features an event FIFO that can record as many as 16 events. By default, the FIFO primarily records key events, such as key press and key release. However, it is possible to configure the general-purpose input (GPI) and logic activity to generate event information on the FIFO as well. An event count, EC[4:0], is composed of five bits and works in tandem with the FIFO so that the user knows how much of the FIFO must be read back at any given time. The FIFO is composed of 16 eight-bit sections that the user accesses by reading the FIFO_x registers. The actual FIFO is not in user accessible registers until a read occurs. The FIFO can be thought of as a “first in first out” buffer that is used to fill Register 0x03 to Register 0x12. The event FIFO is made up of 16 eight-bit registers. In each register, Bits[6:0] hold the event identifier, and Bit 7 holds the event state. With seven bits, 127 different events can be identified. See Table 11 for event decoding. EVENT1[7:0] EVENT8_IDENTIFIER[6:0] EVENT2[7:0] EVENT3[7:0] EVENT4[7:0] EVENT13[7:0] EVENT14[7:0] EVENT15[7:0] EVENT16[7:0] EVENT5[7:0] EVENT6[7:0] EVENT7[7:0] EVENT8[7:0] EVENT9[7:0] EVENT10[7:0] EVENT11[7:0] EVENT12[7:0] 7 EVENT8_STATE GPI EVENTS EC[4:0] OVRFLOW_INT KEY EVENTS LOGIC EVENTS 6 5 4 3 2 1 0 FIFO UPDATE Figure 7. Breakdown of Eventx[7:0] Bits When events are available on the FIFO, the user should first read back the event count, EC[4:0], to determine how many events must be read back. Events can be read from the top of the FIFO only. When an event is read back, all remaining events in the FIFO are shifted up one location, and the EC[4:0] count is decremented. KEY 3 PRESSED KEY 3 RELEASED GPI 7 ACTIVE EC = 3 KEY 3 RELEASED GPI 7 ACTIVE EC = 2 GPI 7 ACTIVE EC = 1 EC = 0 THIRD READ SECOND READ FIRST READ Figure 8. FIFO Operation The FIFO registers (0x03 to 0x12) always point to the top of the FIFO (that is, the location of EVENT1[7:0]). If the user tries to read back from any location in a FIFO, data is always obtained from the top of that FIFO. This ensures that events can only be read back in the order in which they occurred, thus ensuring the integrity of the FIFO system. As stated above, some of the onboard functions of ADP5585 can be programmed to generate events on the FIFO. A FIFO update control block manages updates to the FIFO. If an I2C transaction is accessing any of the FIFO address locations, updates are paused until the I2C transaction has completed. A FIFO overflow event occurs when more than 16 events are generated prior to an external processor reading a FIFO and clearing it. If an overflow condition occurs, the overflow status bit is set. An interrupt is generated if overflow interrupt is enabled, signaling to the processor that more than 16 events have occurred. KEY SCAN CONTROL General The 10 input/output pins can be configured to decode a keypad matrix up to a maximum size of 25 switches (5 × 5 matrix). Smaller matrices can also be configured, freeing up the unused row and column pins for other I/O functions. The R0 through R4 I/O pins comprise the rows of the keypad matrix. The C0 through C4 I/O pins comprise the columns of the keypad matrix. Pins used as rows are pulled up via the internal 300 kΩ (or 100 kΩ) resistors. Pins used as columns are driven low via the internal NMOS current sink. |
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