Hardware Design V1.01(091226)

SIM900 Hardware Design
SDA I/O I
2
C bus data open
KBR0~KBR4 O If unused keep
these pins open
KBC0~KBC4 I
Keypad interface
Pull up to
VDD_EXT, if
unused keep
pins open
Serial port
PIN NAME I/O DESCRIPTION DC CHARACTERISTICS COMMENT
RXD I Receive data
TXD O Transmit data
RTS I Request to send
CTS O Clear to send
RI O Ring indicator
DSR O Data Set Ready
DCD O Data carry detect
DTR I Data terminal Ready
VILmax=0.15 *VDD_EXT
VIHmin=0.85*VDD_EXT
VILmin= 0V
VIHmax= VDD_EXT
VOHmin= VDD_EXT-0.1V
VOLmax=0.1V
VOHmax= VDD_EXT
VOLmin= 0V
DTR Pin has
been pulled
up to
VDD_EXT. If
unused keep
pin open
Debug interface
PIN NAME I/O DESCRIPTION DC CHARACTERISTICS COMMENT
DBG_TXD O
DBG_RXD I
Serial interface for
debugging and firmware
upgrade
VILmax=0.15 *VDD_EXT
VIHmin=0.85*VDD_EXT
VILmin= 0V
VIHmax= VDD_EXT
VOHmin= VDD_EXT-0.1V
VOLmax=0.1V
VOHmax= VDD_EXT
VOLmin= 0V
If unused keep
pins open
SIM interface
PIN NAME I/O DESCRIPTION DC CHARACTERISTICS COMMENT
SIM_VDD O Voltage supply for SIM card The voltage can be select by software
automatically either 1.8V or 3V
SIM_DATA I/O SIM data output
SIM_CLK O SIM clock
SIM_RST O SIM reset
VILmax=0.15 *SIM_VDD
VIHmin=0.85*SIM_VDD
VILmin= 0V
VIHmax= SIM_VDD
VOHmin= SIM_VDD-0.1V
VOLmax=0.1V
VOHmax= SIM_VDD
VOLmin= 0V
All signals of
SIM interface
are protected
against ESD
with a TVS
diode array.
Maximum cable
length 200mm
from the module
SIM900_HD_V1.01 26.12.2009
18