OpenWrt Forum Archive

Topic: [Help] Where is the TTL pin? <RT5350F MIP901>

The content of this topic has been archived on 31 Mar 2018. There are no obvious gaps in this topic, but there may still be some posts missing at the end.

The PCB shows the model is ALK_MIP901_V3.0
But I can't find the TTL pin.
https://cbu01.alicdn.com/img/ibank/2014/067/684/1307486760_2111944351.jpg
https://cbu01.alicdn.com/img/ibank/2013/266/297/1040792662_2111944351.jpg
Flash:8M, Memory:32M

If someone can find the pins, that would be been thankful.

General Features
system solution:    Aplication processor & EVDO Rev.A 3G module & Wi-Fi
3G Band:    CDMA 2000 1X EVDO Rev.A 800/1900 MHz
3G receive sensivity:    CDMA 1X EVDO 800/1900 MHz: -105.5dBm

Output power of 3G module:
CDMA 1X  800/1900 MHz: +23.5dBm
CDMA EVDO 800/1900 MHz: +22.5dBm

Data rate:    CDMA2000 1XEVDO Rev.A: DL 3.1Mbps / UL 1.8Mbps

Wi-Fi standard:     80.211b/g/n, support WAPI

Wi-Fi receive sensivity:
802.11b (-86dBm) at 11Mbps
802.11g (-72dBm) at 54Mbps
802.11n (-72dBm) at 150Mbps

Output power of WIFI:
20dBm(Max) in 11b mode
16dBm(Max) in 11g mode
16dBm(Max) in 11n mode

Battery:     5200mAh Li-ion battery
AC adapter:     DC 5V/1A
Charging mode:     USB or AC adapter

LED indicator:
Status Indicator
WIFI Indicator
WLAN Indicator
Battery Indicator

Dimensions:     78mm*62mm*30mm
Weight:     150g
Operating temperature:     -20℃ - +75℃
Storage temperature:     -40℃ - +85℃
Humidity:     5%~ 95%

Iterface
USB 2.0 HIGH SPEED
T-flash card

SIM slot:
Standard 6 PIN SIM card interface
3V SIM card or 1.8V SIM card

WWAN
Auto WWAN configuration and set up
WWAN - Auto-dial/Always on
WWAN - Dial on demand
WWAN - Manual Dial
WAN Keep-alive capabilities
Failover
APN

Router
Network Address Translation (NAT)
IP Port Forwarding
VPN Pass-through
PPTP/L2TP Client
UPnP
DHCP
IP filter
WIFI control
Domain name service

Security
Firmware Upgradable
Configuration Import/Export
Admin – Web GUI
Help – Web GUI
Set up Wizard
Event Logs
WAN Status/Diagnostic Info (Detail)
NTP
Time Zone
Hide SSID
Basic Firewall Features
WEP Support (64 & 128)
WPA/WPA2 Support
WAPI
MAC/IP Filtering
Content Filtering
WAN port restriction

Application
auto-running of client software
RAS
USSD
Language: English by default (optional)
mobile storage

There aren't exactly a lot of options. The only unused contacts I see, aside from those for the 3G card, are the ones in from the ethernet connector.
I don't think it is the leftmost two, because they seem to be connected to transistors. The third from the right looks like ground. If you have a multimeter check the voltages relative to ground on all the pads with the thing powered up. Pads that are "high" and stable (probably 3.3v) are candidates for the TX, pads that are low are candidates for the RX. Now reboot the board and check if any of the "high" and stable pads are dancing around, or just start probing them with the RX pin on your TTL serial port/converter (set it to 56Kbps 8N1) and look for text during boot. Once you've found it, keep the connection and start probing the low pads with the TX pin on your serial converter. While in contact, hit the return key a few times. When the device responds you've probably found the RX.

The discussion might have continued from here.