XE8000EV108 Semtech, XE8000EV108 Datasheet - Page 75

• Manufacturer Part Number: XE8000EV108
• Description: EVAL BOARD FOR XE8806/XE8807
• Manufacturer: Semtech
• Type: MCUr

Specifications of XE8000EV108

• Contents: Fully Assembled Evaluation Board
• For Use With/related Products: XE88LC06AMI026
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

The timing of the CPU clock (Figure 12-2) depends on the selection of the CpuSel bit in the RegSysClock register
and is given in Table 12-11. f
the 32 kHz depends on the selected clock source (see clock block documentation).
Pins PB[5] and PB[4] can be used for S1 and S0 of the USRT (see USRT documentation) when the UsrtEnable bit
is set in RegUsrtCtrl. The PB[5] and PB[4] then become open-drain. This overrides the values contained in
PBOpen(5:4), PBOut(5:4) and PBDir(5:4). If there is no external pull-up resistor on these pins, internal pull-ups
should be selected by setting PBPullup(5:4). When S0 is an output, the pin PB[4] takes the value of UsrtS0 in
RegUsrtS0. When S1 is an output, the pin PB[5] takes the value of UsrtS1 in RegUsrtS1.
Pins PB[6] and PB[7] can be used by the UART (see UART documentation). When UartEnTx in RegUartCtrl is set
to 1, PB[6] is used as output signal Tx. When UartEnRx in RegUartCtrl is set to 1, PB[7] is used as input signal
Rx. This overrides the values contained in PBOut(7:6) and PBDir(7:6).
12.7 Port B digital capabilities
12.7.1
The direction of each bit within Port B (input only or input/output) can be individually set using the RegPBDir
register. If PBDir[x] = 1, both the input and output buffer are active on the corresponding Port B. If PBDir[x] = 0,
the corresponding Port B pin is an input only and the output buffer is in high impedance. After reset (nresetpconf)
Port B is in input only mode (PBDir[x] are reset to 0).
The input values of Port B are available in RegPBIn (read only). Reading is always direct - there is no debounce
function in Port B. In case of possible noise on input signals, a software debouncer with polling or an external
hardware filter have to be realized. The input buffer is also active when the port is defined as output and the
effective value on the pin can be read back.
Data stored in RegPBOut are outputted at Port B if PBDir[x] is 1. The default values after reset is low (0).
When a pin is in output mode (PBDir[x] is set to 1), the output can be a conventional CMOS (Push-Pull) or a N-
channel Open-drain, driving the output only low. By default, after reset (nresetpconf) the PBOpen[x] in
RegPBOpen is cleared to 0 (push-pull). If PBOpen[x] in RegPBOpen is set to 1 then the internal P transistor in
the output buffer is electrically removed and the output can only be driven low (PBOut[x]=0). When PBOut[x]=1,
the pin is high Impedance. The internal pull-up or an external pull-up resistor can be used to drive to pin high.
Note: Because the P transistor actually exists (this is not a real Open-drain output) the pull-up range is limited to
Each bit can be set individually for pull-up or not using register RegPBPullup. Input is pulled up when its
corresponding bit in this register is set to 1. Default status after (nresetpconf) is 1, which means with pull up. To
limit power consumption, pull-up resistors are only enabled when the associated pin is either a digital input or an N-
channel open-drain output with the pad set to 1. In the other cases (push-pull output or open-drain output driven
low), the pull up resistors are disabled independent of the value in RegPBPullup.
After power-on reset, the Port B is configured as an input port with pull-up. During power-on reset (see reset block
documentation) however, the pin PB[1] is pulled down in stead of pulled up. Once the power-on reset completed,
the pin PB[1] is pulled up, exactly as the other Port B pins.
© Semtech 2006
VDD + 0.2V (avoid forward bias the P transistor / diode).
Port B digital configuration
max
is the frequency of fastest clock present in the circuit. Note that the tolerance on
Table 12-11. CPU clock timing parameters.
CpuSel
0
1
f1
f
f
max
max
12-6
/4
f2
f
32 kHz
max
XE8806A/XE8807A
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