UPD72042BGT NEC [NEC], UPD72042BGT Datasheet - Page 12

• Manufacturer Part Number: UPD72042BGT
• Description: LSI DEVICE FOR Inter Equipment Bus (IEBus) PROTOCOL CONTROL
• Manufacturer: NEC [NEC]

(1) Header
12
Number of bits
Transmission
P : Parity bit (1 bit)
A : Acknowledge bit (1 bit)
N : Number of data bytes
Remark For broadcast, the value of the acknowledge bit is ignored.
Field name
The header consists of a start bit and a broadcast bit. These are explained below.
1
2
Mode 0
Mode 1
When A = 0: ACK
When A = 1: NAK
Start bit
The start bit is a signal used to notify the other units of the beginning of data transmission.
Before a unit starts data transmission, it outputs a low-level signal (start bit) for a specified duration, then
outputs the broadcast bit.
When the unit attempts to output the start bit, another unit may have already output the start bit. In such
a case, the unit does not output the start bit, and instead waits for the other unit to stop outputting the start
bit. Then, synchronized with the completion of start bit output by the other unit, the unit starts output of the
broadcast bit.
All units, except that unit which started the transmission, detect the start bit and become ready for reception.
Broadcast bit
The broadcast bit is used to distinguish between broadcast and ordinary communication.
If the broadcast bit is 0, broadcast is indicated. If the broadcast bit is 1, ordinary communication is indicated.
There are two types of broadcast: group broadcast and general broadcast. These types are distinguished
by the slave address. (For details of the slave address, see (3).)
For broadcast, more than one slave unit can exist as an associated communication station. Therefore, the
acknowledge bits for the master address field and subsequent fields are not returned.
When more than one unit starts sending a communication frame at the same time, broadcast takes
precedence over ordinary communication and wins arbitration.
time
Start
bit
Header
1
Broad-
cast
bit
1
address field
address
Master
Master
12
P
1
Fig. 2-1 Transmission Signal Format
address
Slave
address field
12
Approx. 7330
Approx. 2090
Slave
Data Sheet S13990EJ3V0DS
P
1
A Control
1
s
s
Control field
bits
4
P
1
A
1
length
Data-
Data-length
bits
8
field
1
P
A
1
Data
bits
8
Approx. 1590
Approx. 410
1
P
1
A
Data field
(When f
Data
bits
N
8
N
X
PD72042B
= 6 MHz)
s
s
P
1
A
1