User's Manual l MBa8Xx UM 0100 l © 2020, TQ-Systems GmbH
Page 15
3.4
GPIO port expander
An 8-fold port expander PCA9538A is used to control various components on the MBa8Xx, see Table 12.
The port expander is controlled via I2C1. The address of the port expander can be altered by reassembling resistors.
When changing the address, care must be taken to avoid address conflicts with existing I
2
C devices, see Table 10.
The assembly options are documented in the schematic of the MBa8Xx.
In the initial state after switching on, all ports are set as input and the respective connected component is thus deactivated.
The I/O level of the signals is 1.8 V.
TQMa8Xx
I2C1
PE1_INT#
PCA9538A
8x GPIO
I2C
INT#
IO_[0:7]
Figure 4:
Block diagram GPIO expander
Table 12:
Port expander functions
Port
Signal
Dir.
Remark
IO_0
NC
I
Not connected / reserved
IO_1
LED_A
O
PD
User-LED (see chapter 3.9.5, Status LEDs)
IO_2
LED_B
O
PD
User-LED (see chapter 3.9.5, Status LEDs)
IO_3
NC
I
Not connected / reserved
IO_4
DSI_EN
O
Enable-Signal for eDP bridge, high-active
IO_5
USB_RESET#
O
Not used. Optional as Reset for the USB hub (see Table 18), low-active
IO_6
V_12V_EN
O
Enable signal for 12 V supply (V_12V), high-active
IO_7
PCIE_DIS#
O
Disable signal for Mini PCIe, low-active
The I²C address of the GPIO port expander is determined, among other things, by the input level of pins A0 and A1.
By changing the resistor, the I²C address can be changed according to the following table.
Details can be taken from the MBa8Xx schematics.
Table 13:
Assembly option I²C address GPIO port expander
7-bit-address
R22
R146
R23
R147
Remark
0x70
NP
0 Ω
NP
0 Ω
Default
0x71
0 Ω
NP
NP
0 Ω
–
0x72
NP
0 Ω
0 Ω
NP
–
0x73
0 Ω
NP
0 Ω
NP
–
