參數(shù)資料
型號: 9S12KT256DGV1
英文描述: MC9S12KT256 Device User Guide
中文描述: MC9S12KT256設(shè)備用戶指南
文件頁數(shù): 62/126頁
文件大小: 7307K
代理商: 9S12KT256DGV1
Device User Guide — 9S12KT256DGV1/D V01.09
62
Freescale Semiconductor
2.3.10 PB[7:0] / ADDR[7:0] / DATA[7:0] — Port B I/O Pins
PB7-PB0 are general purpose input or output pins. In MCU expanded modes of operation, these pins are
used for the multiplexed external address and data bus.
2.3.11 PE7 / NOACC / XCLKS — Port E I/O Pin 7
PE7 is a general purpose input or output pin. During MCU expanded modes of operation, the NOACC
signal, when enabled, is used to indicate that the current bus cycle is an unused or “free” cycle. This signal
will assert when the CPU is not using the bus.
The XCLKS is an input signal which controls whether a crystal in combination with the internal Loop
Controlled Pierce (low power) oscillator is used or whether Full Swing Pierce oscillator/external clock
circuitry is used. The state of this pin is latched at the rising edge of RESET. If the input is a logic low the
EXTAL pin is configured for an external clock drive or Full Swing Pierce Oscillator. If input is a logic
high a Loop Controlled Pierce oscillator circuit is configured on EXTAL and XTAL. Since this pin is an
input with a pull-up device during reset, if the pin is left floating, the default configuration is a Loop
Controlled Pierce oscillator circuit on EXTAL and XTAL.
Figure 2-5 Loop Controlled Pierce Oscillator Connections (PE7=1)
Table 2-3 Clock selection based on PE7 during reset
PE7
1
0
Description
Loop Controlled Pierce Oscillator selected
Full Swing Pierce Oscillator or external clock selected
MCU
EXTAL
XTAL
VSSPLL
Crystal or
ceramic resonator
C
8
C
7
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