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RS232/LIN

The RS-232/LIN plugin implements level conversion between the core board's inverse-TTL USARTs and standard RS-232 levels, allowing the connection of up to 2 standard RS-232 serial devices. Alternatively, it can be configured as a master node for a LINBus network.

Bare RS232/LIN board.

Description [size] Format
Circuit schematic [11.4KB] Adobe Acrobat PDF
PCB layout [75.8KB] Adobe Acrobat PDF

For RS-232 level conversion, the Maxim MAX3232 chip is used. This features onboard charge-pumps, generating the +/- 12v levels required for RS-232 from the +3.3v supply.

For LINBus connectivity, the Maxim MAX13021 chip is used. External power must be supplied to power the LIN network, this can be anything from 5v up to 38v.

Interface

The plugin is designed to interface with the Lettuce-v1 core board via the USART header. The two RS-232 channels can be enabled independently, and pass-through connections are available on the plugin board. This allows one channel to be used as RS-232 and the other as inverse-TTL, or any combination as required. If the plugin is used in LINBus mode, RS-232 or pass-through inverse-TTL functionality is not available.

Pass-through USART header

Dual Inverse-TTL USART header, identical to that on the core board.

RS-232 headers

This is the standard 2x5-pin RS-232 header found on many PC motherboards and IO cards. Ribbon cables converting these to standard 9 pin "D" connectors are readily available from computer suppliers and are often bundled with PC motherboards.

The RS-232 connector is implemented as follows:

Pin Name Purpose
1 DCD Data carrier detect
2 DSR Data set ready
3 RXD Receive data
4 RTS Request to send
5 TXD Transmit data
6 CTS Clear to send
7 DTR Data terminal ready
8 RI Ring indicator
9 Gnd Ground
10 NC Not connected

Note: These pin numbers are the same as a standard 9 pin "D" serial connector, so an adaptor simply connects pin-to-pin (pin 10 is not used).

LINBus header

Three identical LINBus connectors are provided in order to allow easy connection of LINBus devices.

The LINBus connector is implemented as follows:

Pin Name Purpose
1 LIN LINBus data
2 +V LINBus power (5-38v)
3 Gnd Ground

LINBus power header

The LINBus power connector is used to supply power to the LIN network, which can be used to power the device nodes.

The LINBus power connector is implemented as follows:

Pin Name Purpose
1 +V LINBus power in (5-38v)
2 Gnd Ground

Component list

Below is a full list of components required to build the RS-232/LIN plugin board.

ICs

ID Value Package Description
U1 MAX3232 SO16 RS-232 level converter
U2 MAX13021 SO8 LIN transceiver
U3 78L05 TO-92 +5v 100mA regulator

Connectors

ID Type Description
J1 2x4 100mil R/A socket Core USART socket
J2 1x4 100mil header !TTL USART channel 1
J3 1x4 100mil header !TTL USART channel 2
J4 2x5 100mil header RS-232 channel 1
J5 2x5 100mil header RS-232 channel 2
J6 1x2 100mil header LINBus power
J7 0603 solder jumper RS-232 channel 1 enable
J8 0603 solder jumper RS-232 channel 1 enable
J9 0603 solder jumper RS-232 channel 2 enable
J10 0603 solder jumper RS-232 channel 2 enable
J11 0603 solder jumper LINBus enable
J12 0603 solder jumper LINBus enable
J13 0603 solder jumper LINBus enable
J14 0603 solder jumper LINBus enable
J15 1x3 100mil header LINBus
J16 1x3 100mil header LINBus
J17 1x3 100mil header LINBus

Capacitors

ID Value Package Description
C1 100nF 0805 Supply decoupling
C2 100nF 0805 Reqd by MAX3232
C3 100nF 0805 Reqd by MAX3232
C4 100nF 0805 Reqd by MAX3232
C5 100nF 0805 Reqd by MAX3232
C6 100nF 0805 LINBus decoupling

Resistors

ID Value Package Description
R1 1K 0805 LINBus pull-up
R2 10K 0805 LIN RXD pull-up
R3 5K 0805 LIN NWAKE pull-up

Misc

ID Value Package Description
D1 1N4148 300mil axial LINBus pull-up protection
Updated on 2010-04-25 13:41:59 +0000 | Requested on 2020-10-27 11:57:28 +0000