LTP5901-IPR datasheet(24/34 Pages) LINER

24 / 34 page

LTP5901-IPR/LTP5902-IPR

59012iprfa

For more information www.linear.com/LTP5901-IPR or www.linear.com/LTP5902-IPR

operaTion

32.768kHz Crystal

Once Eterna is powered up and the 32.768kHz crystal

source has begun oscillating, the 32.768kHz crystal re-

mains operational while in the active state, and is used as

the timing basis when in doze state. See the State Diagram

section, for a description of Eterna’s operational states.

20MHz Crystal

The 20MHz crystal source provides a frequency reference

for the radio, and is automatically enabled and disabled

by Eterna as needed.

RADIO

Eterna includes the lowest power commercially available

2.4GHz IEEE 802.15.4e radio by a substantial margin.

(Please refer to section Radio Specifications, for power

consumption numbers). Eterna’s integrated power ampli-

fier is calibrated and temperature-compensated to con-

sistently provide power at a limit suitable for worldwide

radio certifications. Additionally, Eterna uniquely includes

a hardware-based autonomous MAC that handles precise

sequencing of peripherals, including the transmitter, the

receiver, and advanced encryption standard (AES) periph-

erals. The hardware-based autonomous media access

controller (MAC) minimizes CPU activity, thereby further

decreasing power consumption.

UARTS

The principal network interface is through the applica-

tion programming interface (API) UART. A command-line

interface (CLI) is also provided for support of test and

debug functions. Both UARTs sense activity continuously,

consuming virtually no power until data is transferred over

the port and then automatically returning to their lowest

power state after the conclusion of a transfer. The defini-

tion for packet encoding on the API UART interface can

be found in the SmartMesh IP Manager API Guide and the

CLI command definitions can be found in the SmartMesh

IP Manager CLI Guide.

API UART PROTOCOL

The API UART protocol was created with the goal of sup-

portingawiderangeofcompanionmultipointcontrolunits

(MCUs)whilereducingpowerconsumptionofthesystem.

The receive half of the API UART protocol includes two ad-

ditional signals in addition to UART_RX: UART_RX_RTSn

and UART_RX_CTSn. The transmit half of the API UART

protocol includes two additional signals in addition to

UART_TX: UART_TX_RTSn and UART_TX_CTSn. The

API UART protocol is referred to as Mode 4.

In the figures accompanying the protocol descriptions,

signals driven by the companion processor are drawn

in black and signals driven by Eterna are drawn in blue.

UART Mode 4

UART Mode 4 incorporates level-sensitive flow control

on the TX channel and requires no flow control on the

RX channel, supporting 115200 baud. The use of level-

sensitive flow control signals enables higher data rates

with the option of using a reduced set of the flow control

signals; however, Mode 4 has specific limitations. First,

the use of the RX flow control signals (UART_RX_RTSn

and UART_RX_CTSn) for Mode 4 are optional provided

the use is limited to the industrial temperature range

(–40°C to 85°C); otherwise, the flow control is mandatory.

If RX flow control signals are not used, UART_RX_RTSn

shouldbetiedtoVSUPPLY(inactive)andUART_RX_CTSn

should be left unconnected. Second, unless the com-

panion processor is always ready to receive a packet,

the companion processor must negate UART_TX_CTSn

prior to the end of the current packet. Failure to negate

UART_TX_CTSn prior to the end of a packet may result

in back to back packets. Third, the companion processor

must wait at least tRX_INTERPACKET between transmitting

packets on UART_RX. See the UART AC Characteristics

section for complete timing specifications. Packets are

HDLC encoded with one stop bit and no parity bit. The flow

control signals for the TX channel are shown in Figure 11.

TransfersareinitiatedbyEternaassertingUART_TX_RTSn.

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