SIM I/O接上拉电阻的原因

也可以减少干扰

查查SIM卡的规范，你就会发现答案！

我认为：可以稳定IO上的信号，同时也可以更多的读卡器的IO阻抗匹配

最近仔细查看资料，认为SIM I/O都要接上拉电阻，主要与SIMVCC电压和处理器I/O电平不一致，通过内部电路和上拉电阻到SIMVCC,使得两者电平能够转换，这是本人的一点想法，请工程师们给予评论。

未必,我们公司的就不用上拉电阻

同意楼上的观点，
查阅一些电路，包括一般的GSM手机及smartphone，发现很少用上拉电阻的。
倒是不少的手机会串连电阻做阻抗匹配。
Sagem的XS200上面在外围电路上面就没有任何上下拉电阻或者串连电阻。
小弟的拙见是问题的焦点还是集中在SIM card的interface module上面。
欢迎大家进一步交流
whfrog107@msn.com

补充说明：
例如MTK平台的solution，虽然外围电路没有设计上拉电阻，但是其SIM card的interface module里面集成了pull high电阻。
还是希望大家多去查阅了解platform solution的相关datasheet。

为了在平台和SIM card之间的电平一致,小弟拙见.

你可以认为SIM 卡接口就是I2C
PullUp Res已经集成在了HOST IO内部

请看这个
* I/O
This contact is used as input (reception mode) or output (transmission mode) for data exchange. Two possible states exist for I/O:
- mark or high state (State Z), if the card and the interface device are in reception mode or if the state is imposed by the transmitter.
- space or low state (State A), if this state is imposed by the transmitter.
When the two ends of the line are in reception mode, the line shall be maintained in state Z. When the two ends are in non-matced transmit mode, the logic state of the line may be indeterminate. During
operations, the interface device and the card shall not both be in transmit mode.
Table 1 - Electrical characteristics of I/O under normal ------- operation conditions.
,--------+--------------------------------+---------+---------+------,
| Symbol | Conditions | Minimum | Maximum | Unit |
+--------+--------+-----------------------+---------+---------+------+
| | Either | Iih max = +/- 500uA | 2 | VCC| V|
|Vih | (1)+-----------------------+---------+---------+------+
| | or | Iih max = +/- 50uA | 0.7 VCC | VCC (3) | V|
+--------+--------+-----------------------+---------+---------+------+
|Vil | Iil max = 1mA | 0 | 0.8| V|
+--------+--------------------------------+---------+---------+------+
| | Either | Iol max = +/- 100uA | 2.4 | VCC| V|
|Voh | +-----------------------+---------+---------+------+
| (2) | or | Iol max = +/- 20uA | 3.8 | VCC| V|
+--------+--------+-----------------------+---------+---------+------+
|Vol | Iol max = 1mA | 0 | 0.4| V|
+--------+--------------------------------+---------+---------+------+
| tr, tf | Cin = 30pF; Cout = 30pF | | 1| us |
+--------+--------------------------------+---------+---------+------+
| (1) For the interface device, take into account both conditions. |
| (2) It is assumed that a pull up resistor is used in the interface |
| device (recommended value 20k Ohm. |
| (3) The voltage on I/O shall remain between 0.3V and VCC+0.3V. |
'--------------------------------------------------------------------'