About the module Multiplexed GPIO
ConnectCore for i.MX51 Hardware Reference Manual
52
Channel ADC Mode Touch Screen Mode Touch Screen Inactive Mode
0 Battery Voltage Touch_X1 -
1 Battery Current Touch_X2 -
2 Application voltage (VBP) - -
3 Charger Voltage Touch_Y1 -
4 Charger Current Touch_Y2 General Purpose via TOUCH_X1
5 Battery Temperature Monitoring - General Purpose via TOUCH_X2
6 General Purpose ADIN6 Contact resistance General Purpose via TOUCH_Y1
7 General Purpose ADIN7 Contact resistance General Purpose via TOUCH_Y2
The ADC Mode, Touch Screen Mode and Touch Screen Inactive Mode are selected using the ADSEL,
TSMOD0, TSMOD1 and TSMOD2 bits in the Freescale MC13892 Power Management chip.
Channel 5 in ADC mode connects via ADIN5 but this is typically where a Thermistor is used to monitor
the battery pack temperature. When battery temperature monitoring is not required, this input can
be used as a general purpose ADC input but with the following considerations:
1. The power-up default state is for temperature monitoring via the Thermistor. The IMX51
module contains a resistor divider to apply the right bias to the ADIN5 pin to allow the unit to
boot correctly (without requiring a Thermistor to be fitted). The software will first need to
disable this function after which the analogue input may be connected to ADIN5. Once this is
disabled, the real analogue input may be connected via this pin.
2.
The presence of the resistor divider appears like a 5kΩ load, it follows that the tri-state buffer
used to drive this input will need to have an output impedance of less than 5Ω if the 10-bit
resolution is not to be compromised. An alternative approach is to disable the GPO1 pin of the
MC13892 in software and use that pin as the input. In that case the input impedance will look
like 20kΩ to GND. Therefore the tri-state buffer output impedance now needs to be 20Ω or
lower. However this way results in the real input voltage being divided by 2 on the ADC input.
When using GPO1 as the input, do not connect anything to ADIN5.
Channel 6 in ADC mode may also monitor the Coin-cell input voltage.
Channel 7 in ADC mode may also monitor the Die Temperature. Please note the UID voltage cannot be
read nor is alternative input ADIN7B available.
It is possible to support 7 ADC channels by alternating between the ADC mode and Touch Screen
Inactive mode.
For more information refer to the datasheet of the Freescale MC13892 Power Management chip.
Synchronous Serial Interface (SSI)
The ConnectCore for i.MX51 module provides up to three synchronous serial interfaces (SSI) that
allows communicating with a variety of serial devices as standard CODECs, audio CODECs
implementing the I
2
S standard and Intel AC97 standard.
SSI is typically used to transfer samples in a periodic manner. The SSI consists of independent
transmitter and receiver sections with independent clock generation and frame synchronization.
The main features of the SSI interface are the following:
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