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COM Express Interfaces

2.20. General Purpose Serial Interface

Since Revision 2.0 of the COM Express specification two optional serial ports are available on

Type 10 and Type 6 COM Express Modules uses pins on the A-B connector that have been

reclaimed from the A-B VCC_12V pool. As such, it is possible that if a Type 6 or 10 Module is

deployed in an R1.0 Carrier Board for Module Types 1,2,3,4,5 then the Module TTL level serial

pins may be exposed to the 12V supply, and Module designers must plan for this. Similarly, an

R1.0 Module deployed on an R2.0 Carrier may bridge 12V to the serial pins and Carrier

designers must plan for this. These pins are designated SER0_TX, SER0_RX, SER1_TX and

SER1_RX. Data out of the Module is on the _TX pins. Please refer to section 2.22.10

'Protecting COM.0 Pins Reclaimed From the VCC_12V Pool' on page 144 below. Hardware

handshaking and hardware flow control are not supported.

2.20.1. Signal Definitions

Table 39: General Purpose Serial Interface Signal Definition

Signal Pin Description I/O

SER0_TX A98 Transmit Line for Serial Port 0 O CMOS (protected)

SER0_RX A99 Receive Line for Serial Port 0 I CMOS (protected)

SER1_TX A101 Transmit Line for Serial Port 1 (can be shared with CAN function) O CMOS (protected)

SER1_RX A102 Receive Line for Serial Port 1 (can be shared with CAN function) I CMOS (protected)

In Revision 2.0 of COM Express Specification these signals have been reclaimed from the

VCC_12V pool. Therefore protection on the Module and on the Carrier Board is necessary to

avoid damage to those when accidentally exposed to 12V.

PICMG

COM Express

Carrier Board Design Guide Rev. 2.0 / December 6, 2013

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