User manual

Page 13

Document No. 80-15151 Issue 6 HEBER LTD

5.8 Memory Expansion

Various optional memory cards may be fitted to the Memory Expansion Connector P15. Seven lines

from the FPGA are included along with 16 data lines and 21 address lines.

The default functionality of the FPGA lines allows memory cards fitted with up to 4 EPROM or FLASH

devices to be accommodated along with a pair of RAM devices with no additional mapping

components.

If a memory card is fitted with 5V FLASH devices, then Write facilities are available. EPROM

Autoselect is also available with devices fitted on a Memory Card.

5.9 Open Drain Outputs, OP0-63

A block of 64 Open Drain Outputs, OP0-63, are provided by 8 off TPIC6259 devices U22-U29 (see

Schematic Sheet 6 - Outputs).

These are memory mapped as the least significant byte of a block of 8 words of address space. The

chip select for these devices, CS_OP-, is provided by the FPGA. Consult the User Manual of the

FPGA being used for exact mapping.

Please note that the chips are bit wide, not byte wide. Thus, Bit 0 of each word drives one device,

U22: Bit 1 drives U23, etc.

Table 10. Mapping of Open Drain Outputs (OP0-63) to TPIC6259 Devices

Bit D7 D6 D5 D4 D3 D2 D1 D0

U29 U28 U27 U26 U25 U24 U23 U22 Addr.

OP63 OP62 OP61 OP60 OP59 OP58 OP57 OP56 Base+14

OP55 OP54 OP53 OP52 OP51 OP50 OP49 OP48 Base+12

OP47 OP46 OP45 OP44 OP43 OP42 OP41 OP40 Base+10

OP39 OP38 OP37 OP36 OP35 OP34 OP33 OP32 Base+8

OP31 OP30 OP29 OP28 OP27 OP26 OP25 OP24 Base+6

OP23 OP22 OP21 OP20 OP19 OP18 OP17 OP16 Base+4

OP15 OP14 OP13 OP12 OP11 OP10 OP9 OP8 Base+2

OP7 OP6 OP5 OP4 OP3 OP2 OP1 OP0 Base+0

Basically, the drive capability of these devices is 250mA per output, continuous, with all outputs ON. If

less than 8 outputs are ON in any one package, or any outputs are operating with a small load, the

capacity of the other outputs increases. For example, at 25°C, the TPIC6259 can sink 400mA

continuously from 3 outputs. Please refer to the data sheet for the TPIC6259 (tpic6259.pdf) for

details.

When allocating any output to a load greater than 250mA, consideration should be given to the

loading on each device. See Section 6.1, “Driving Reels” for details on driving standard reel

mechanism stepper motors.

Note also that, because they are MOSFETs, the outputs are resistive (<2Ω ) and do not suffer from the

minimum saturation voltage of about 1V which would be the case if they were darlingtons. Therefore,

at low currents, they pull down close to Gnd and may be safely used to drive TTL Inputs, Switch

Strobes, Coin Mechanism Enables, etc.