UPD6708GS 데이터 시트보기 (PDF) - NEC => Renesas Technology
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UPD6708GS Datasheet PDF : 72 Pages
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µPD6708
2.3 Transfer Protocol
The IEBus transfer signal format is shown in Figure 2-1.
Data is transferred as a series of signals called a communication frame. The number of data that can be transferred in
one communication frame and the transfer speed differ depending on the communication mode.
Figure 2-1. Transfer Signal Format
(fx = at 12 MHz)
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Field Name Header
Master Slave Address Control Field Message
Data Field
Address Field
Field
Length Field
Number of Bits 1 1
12 1 12 1 1 4 1 1 8 1 1 8 1 1
8 11
Start
Broad-
cast
Master
P
Slave
P
A Control P
A
Message
Length
P
A
Data
PA
Bit Bit Address
Address
Bit
Bit
Bit
Data P A
Bit
Transfer Time
Mode 0
Mode 1
Mode 2
Approx. 7330 µs
Approx. 2090 µs
Approx. 1590 µs
Approx. 1590 × N µs
Approx. 410 × Nµs
Approx. 300 × Nµs
P: Parity bit (1 bit)
A: Acknowledge bit (1 bit)
When A = 0: ACK
When A = 1: NAK
N: Number of data bytes
Remark In broadcast communication, the value of the acknowledge bit is ignored.
(1) Header
A header comprises a start bit and a broadcast bit, as described below.
<1> Start bit
The start bit is a signal which tells the other units that data transmission will start.
The unit which is about to start transmitting data will output the low signal (the start bit) for a specified time, and then
outputs the broadcast bit.
If another unit is already outputting a start bit before one unit outputs a start bit, the unit will not output the start bit.
It will wait until the another unit completely outputs the start bit, and then outputs the broadcast bit.
The units other than the one that has started transmission detect this start bit and enters the reception state.
<2> Broadcast bit
The broadcast bit distinguishes between broadcast communication and ordinary communication.
When this bit is ‘0’, it indicates broadcast communication; when it is ‘1’, it indicates ordinary communication. There
are two types of broadcast communication: group broadcast and general broadcast. These types are identified by the
value of the slave address (for the slave address, see (3) “Slave address field”).
In broadcast communication, there are a number of slave units. Therefore, the acknowledge bit is not returned in the
fields described in (2) below and onward.
If two or more units start to transmit a communication frame simultaneously, broadcast communication takes
precedence over ordinary communication, and wins in the arbitration.
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