Serial Ports Troubleshooting of CPU cards
Introduction: Serial ports which is so called the COM ports. It is the basic portion of computer communication. Each computer system usually allocates with 2 com ports. In most of industrial CPU cards, the second port usually designed to be equipped RS-232, RS-422 and RS-485, and it can be adjust by jumper setting. In the early computer, UART 8250 chip is the controller of serial ports, but now it is built-in the super I/O chip. However, most com ports damage is caused by abnormal current input. Such as this current input can easily destroy the inverter of com ports, even the super I/O chip.
Operation Principle: The data transfer mode of com ports can be RS-232, RS-422 and RS-485. To understand how serial ports work, we have to know all the relative chips, include super I/O chip and inverter IC. The following figures shown us the necessary information: 1. The configuration of serial ports in computer system 2. The pin assignment of serial ports in super I/O. 3. The connector modules of serial ports. 4. Loopback wiring diagram of RS-232 and RS-422. 5. Serial Port Timing chart.
Figure-1: Configuration of serial ports
Sy stem Bus
Super I/O C hipset
Inv erter IC
C OM Ports
*Super I/O chips: SMC-37C665/37C651, UMC-8663/8669. *Inverter IC: UMC-8667, GD75232, MAX211/213/241.
Figure-2:Pin assignment of serial port in Super I/O
I I I I I I I I I I I/O I/O I/O I/O I/O I/O I/O I/O I I I I
28 29 30 31 32 33 34 41 42 43 48 49 50 51 53 54 55 56 57 58 44 45
A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 D0 D1 D2 D3 D4 D5 D6 D7 R ESET PW GOD IOR IOW
AEN IR Q3 IR Q4 VC C GND DTR 2C TS2R TS2DSR 2TXD2 R XD2 DC D2R I2DC D1R I1DTR 1C TS1R TS1DSR 1TXD1 R XD1
46 37 38
93 92 91 90 89 88 87 86 85 84 83 82 81 80 79 78
I O O I I O I O I O I I I I I O I O I O I
Figure-3:Connector modules of serial ports
DCD RXD TXD DTR C1 C2 C3 C4 GND DCD RXD TXD DTR GND 485TX+ 485RX+ DSR RTS CTS RI N/C 485TX485TX-
DSR RTS CTS RI C5 C6 C7 C8
DCD TX GND RTS RI
RX DTR DSR CTS N/C
DCD RXD TXD DTR GND
DSR RTS CTS RI NC
Figure-4:Loopback wiring of serial ports
RS-232 Loop Back
RS-422 Loop Back
Figure-5:Serial port timing chart
IOW t1 RTSx, DTRx IRQx CTSx, DSRx, DCDx t2 IRQx IOW t3 IRQx IOR t4 t5
Parameter t1 t2 t3 t4 t5 t6 RTSx,DTRx Delay from IOW IRQx Active Delay from CTSx, DSRx, DCDx IRQx Interactive Delay from IOR(Leading Edge) IRQx Interactive Delay from IOW(Trailing Edge) IRQx Interactive Delay from IOW IRQx Active Delay from RIx
min typ max units 200 100 120 125 10 100 100 ns ns ns ns ns ns
FAQ: In facts, it is easy to diagnose the serial ports only if you have the tools. The best way to do diagnose is use the external loopback. Here are some test ways help you to check your com ports: 1. Check the port connector is good. 2. Please check your jumper setting very carefully. 3. With external loopback, you can test it via some test programs, such as AMIDIAG, QAPLUS, CHECKIT, COMTEST, etc. All these programs have built up detail functions of com port, but due to the construction of Data transfer mode is different between RS-232/422/485, this test is just available on RS-232 and RS-422. 4. Check the capacities (Fig-3, Type 1) and converter is good or not. 5. Check the super I/O chip is good or not, see Fig-5. 6. Check the clock oscillator and reset are good or not.
Note: 1.To check RS-485, user can use 2 RS-485 ports, and just to do port to port transmission test in the diagnostic Programs. Or if you have Advantech ADAM 4000/5000 series, connect it with DATA+/-, then operate the ADAM utility. If the port is good, you'll find the ADAM module be shown on your monitor. 2. The following instruction is for how to use COMTEST
Component Acer 5105 SMC 37C665 UMC 8663 UMC 8669 UMC 8667 26LS31 26LS32 MAX 211 MAX 213 MAX 241 LT 485 1488D 1489D C150P C220P Major parts list Faulty Phenomena No display, Peripherals(HDD, Serial ports…) unworkable No display, Peripherals(HDD, Serial ports…) unworkable Serial ports unworkable Serial ports unworkable No display, Serial ports unworkable Serial ports unworkable Serial ports unworkable Serial ports unworkable Serial ports unworkable Serial ports unworkable Serial ports (422/485) unworkable Serial ports unworkable Serial ports unworkable Serial ports unworkable Serial ports unworkable Part number 14S4510500 14S4066500 14S4866300 14S4866900 14S4866710 14S5A63100 14S5A63200 14S4021100 14S4021300 1445024100 14S4048500 14S4148800 14S4148900 1124515150 1124522105
COMTEST USER GUIDELINE
PS. Only have to set the correct I/O Address, and don't care about the card type selection.
One Port Test: (Loopback Test)
Step1: Select the right I/O address, Portocol, and IRQ in the "Setting" Step2: Making External Loopback Connector RS-232 : 2-3, 4-6, 7-8 (Self pin to pin wired) RS-422 : 1-4, 2-3, 6-9, 7-8 (Self pin to pin wired) Step3: Enter "Diagnose" to execute loopback test
Internal Loopback : -> If fails, it maybe caused by UART component
External Loopback : RTS-CTS Loop Test -> If fails, please check RTS-CTS Loop DTR-DSR Loop Test -> If fails, please check DTR-DSR Loop IRQ Interrupt Test -> If fails, check with other device or super I/O for the IRQ conflict Data Test (Self send and receive data) -> If fails, please check RxD-TxD Loop.
Two Ports Test: (Port to Port Test) Step1: Select the right I/O address, Protocol, and IRQ in the "Setting" Step2: Making Port to Port Connector (The following wiring such as "2-3" means Port A pin2 wired to Port B pin3) RS-232 : 2-3, 3-2, (Wiring to each other) RS-422 : 1-4, 2-3, 3-2, 4-1, 6-9, 7-8, 8-7, 9-6 (Wiring to each other) RS-485 : Pin to Pin, ( Ex. 1-1, 2-2) Step3: Enter "Diagnose" for Loopback Test Port To Port : Connect ports with loopback as above, then you'll see Port A send a string from A to Z to Port B, and Port B will send back the same string later. If fails, please do One Port Test again.
Terminal Emulation Test : This emulation required two systems for data transmission test. The wiring is the same as Two Port Test. Step1: Select the right I/O address, Protocol, and IRQ in the "Setting" Step2: Enter Terminal Emulation Step3: The upper window is for sending string and the lower window is for receiving data. Whatever the string you send, you can also see the status for receiving in the other computer. Otherwise, there must be some error in the systems, check the wiring and setting or do One Port Test again.